diff --git a/lib/problems.rb b/lib/problems.rb
index 5085953d..a7eb51aa 100644
--- a/lib/problems.rb
+++ b/lib/problems.rb
@@ -1,13 +1,55 @@
 require_relative './stack.rb'
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(n) 
 def balanced(string)
-  raise NotImplementedError, "Not implemented yet"
+  braces_stack = Stack.new
+  string.each_char do |n|
+    case n 
+    when "("
+      braces_stack.push(n)
+    when "{"
+      braces_stack.push(n)
+    when "["
+      braces_stack.push(n)
+    when ")"
+      return false if !stack_checker(braces_stack, "(")
+    when "}"
+      return false if !stack_checker(braces_stack, "{")
+    when "]"
+      return false if !stack_checker(braces_stack, "[")
+    end 
+  end 
+  return braces_stack.empty? 
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+def stack_checker(stack, expected_paren)
+  return !(stack.empty? || stack.pop != expected_paren)
+end 
+
+# Time Complexity: O(n)
+# Space Complexity: O(n) <- but we'd probably use less assuming the expression contains operators
 def evaluate_postfix(postfix_expression)
-  raise NotImplementedError, "Not implemented yet"
+  stack = Stack.new
+  postfix_expression.each_char do |n|
+    if /\+|-|\*|\//.match(n)
+      stack_operation_helper(stack, stack.pop, stack.pop, n)
+    else 
+      stack.push(n)
+    end 
+  end 
+  return stack.pop
 end
+
+def stack_operation_helper(stack, first_pop, second_pop, operator)
+  case operator
+  when "+"
+    stack.push(second_pop.to_i + first_pop.to_i)
+  when "-"
+    stack.push(second_pop.to_i - first_pop.to_i)
+  when "*"
+    stack.push(second_pop.to_i * first_pop.to_i)
+  when "/"
+    stack.push(second_pop.to_i / first_pop.to_i)
+  end 
+end 
diff --git a/lib/queue.rb b/lib/queue.rb
index 828217c6..ab22fc48 100644
--- a/lib/queue.rb
+++ b/lib/queue.rb
@@ -1,31 +1,64 @@
 class Queue
-
+  
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = Array.new(10)
+    @front = 0
+    @back = 0
   end
-
+  
   def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+    #resize if the array is full
+    if @front == (@back + 1) % @store.length
+      temp = Array.new(@store.length + 1) 
+      if @front > @back 
+        temp.each_index do |n|
+          if n < @front
+            temp[n] = @store[n]
+          elsif n > @front
+            temp[n] = @store[n-1]
+          end 
+        end 
+        @front += 1
+      else 
+        temp.each_index do |n|
+          temp[n] = @store[n]
+        end 
+      end 
+      @store = temp
+    end 
+    #add the element
+    @store[@back] = element
+    @back = (@back + 1) % @store.length 
   end
-
+  
   def dequeue
-    raise NotImplementedError, "Not yet implemented"
-  end
-
+    if @front != @back 
+      temp = @store[@front]
+      @store[@front] = nil
+      @front = (@front + 1) % @store.length
+      return temp
+    end
+  end 
+  
   def front
-    raise NotImplementedError, "Not yet implemented"
+    return @store[@front]
   end
-
+  
   def size
-    raise NotImplementedError, "Not yet implemented"
+    return abs(@back - @front + 1)
   end
-
+  
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @front == @back
   end
-
+  
   def to_s
-    return @store.to_s
+    temp = []
+    curr = @front
+    until curr == @back
+      temp << @store[curr] if @store[curr]
+      curr = (curr + 1) % @store.length
+    end 
+    return "#{temp}"
   end
 end
diff --git a/lib/stack.rb b/lib/stack.rb
index cfc6ef0f..ef61f09d 100644
--- a/lib/stack.rb
+++ b/lib/stack.rb
@@ -1,19 +1,20 @@
+require_relative '../lib/linked_list'
+
 class Stack
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = LinkedList.new
   end
 
   def push(element)
-    raise NotImplementedError, "Not yet implemented"
+    @store.add_last(element)
   end
 
   def pop
-    raise NotImplementedError, "Not yet implemented"
+    @store.remove_last()
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @store.empty?
   end
 
   def to_s
diff --git a/test/problems_test.rb b/test/problems_test.rb
index f851f1d2..0cae4fb5 100644
--- a/test/problems_test.rb
+++ b/test/problems_test.rb
@@ -7,37 +7,31 @@
 describe "Test wave 3 problems" do
   describe "balanced" do
     it "Given balanced strings it should return true" do
-      skip
       expect(balanced('(({}))')).must_equal true
     end
 
     it "regards an empty string as balanced" do
-      skip
       expect(balanced('')).must_equal true
     end
 
     it "will return false for an unbalanced set of parens" do
-      skip
       expect(balanced('(()')).must_equal false
       expect(balanced('(()}')).must_equal false
       expect(balanced('([]]')).must_equal false
     end
 
     it "also works for {} and []" do
-      skip
       expect(balanced('[]')).must_equal true
       expect(balanced('{}')).must_equal true
     end
 
     it "also works if the string has opens and closes in the beginning and end" do
-      skip
       expect(balanced('[]()')).must_equal true
     end
   end
 
   describe "postfix" do
     it "can add a 2 numbers together" do
-      skip
       expect(evaluate_postfix("34+")).must_equal 7
       expect(evaluate_postfix("34*")).must_equal 12
       expect(evaluate_postfix("34-")).must_equal -1
@@ -45,7 +39,6 @@
     end
 
     it "can add a evaluate a more complicated expression" do
-      skip
       expect(evaluate_postfix("34+2*")).must_equal 14
       expect(evaluate_postfix("34*2/")).must_equal 6
       expect(evaluate_postfix("34-1+")).must_equal 0
diff --git a/test/queue_test.rb b/test/queue_test.rb
index 8a7dcd9c..197b3578 100644
--- a/test/queue_test.rb
+++ b/test/queue_test.rb
@@ -7,65 +7,67 @@
 describe "Test Queue Implementation" do
   it "creates a Queue" do
     q = Queue.new
-    q.class.must_equal Queue
+    expect(q.class).must_equal Queue
   end
-
+  
   it "adds something to an empty Queue" do
-    skip
     q = Queue.new
     q.enqueue(10)
-    q.to_s.must_equal "[10]"
+    expect(q.to_s).must_equal "[10]"
   end
-
+  
   it "adds multiple somethings to a Queue" do
-    skip
     q = Queue.new
     q.enqueue(10)
     q.enqueue(20)
     q.enqueue(30)
-    q.to_s.must_equal "[10, 20, 30]"
+    expect(q.to_s).must_equal "[10, 20, 30]"
   end
-
+  
   it "starts the size of a Queue at 0" do
-    skip
     q = Queue.new
-    q.empty?.must_equal true
+    _(q.empty?).must_equal true
   end
-
+  
+  it "a Queue is empty after removing all the elements" do
+    q = Queue.new
+    q.enqueue(5)
+    q.enqueue(6)
+    expect(q.dequeue).must_equal 5
+    expect(q.dequeue).must_equal 6
+    expect(q.empty?).must_equal true
+  end
+  
   it "removes something from the Queue" do
-    skip
     q = Queue.new
     q.enqueue(5)
     removed = q.dequeue
-    removed.must_equal 5
-    q.empty?.must_equal true
+    _(removed).must_equal 5
+    _(q.empty?).must_equal true
   end
-
+  
   it "removes the right something (LIFO)" do
-    skip
     q = Queue.new
     q.enqueue(5)
     q.enqueue(3)
     q.enqueue(7)
     removed = q.dequeue
-    removed.must_equal 5
-    q.to_s.must_equal "[3, 7]"
+    _(removed).must_equal 5
+    _(q.to_s).must_equal "[3, 7]"
   end
-
+  
   it "properly adjusts the size with enqueueing and dequeueing" do
-    skip
     q = Queue.new
-    q.empty?.must_equal true
+    _(q.empty?).must_equal true
     q.enqueue(-1)
     q.enqueue(-60)
-    q.empty?.must_equal false
+    _(q.empty?).must_equal false
     q.dequeue
     q.dequeue
-    q.empty?.must_equal true
+    _(q.empty?).must_equal true
   end
-
+  
   it "returns the front element in the Queue" do
-    skip
     q = Queue.new
     q.enqueue(40)
     q.enqueue(22)
@@ -92,7 +94,6 @@
     q.enqueue(130)
     q.enqueue(140)
     q.enqueue(150)
-    q.enqueue(150)
     q.enqueue(160)
     q.enqueue(170)
     q.enqueue(180)
@@ -100,7 +101,7 @@
     q.enqueue(200)
     q.enqueue(210)
     q.dequeue
-
-    expect(q.to_s).must_equal('[40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240]')
+    
+    expect(q.to_s).must_equal('[40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210]')
   end
-end
+end
\ No newline at end of file
diff --git a/test/stack_test.rb b/test/stack_test.rb
index df5046c8..ae31478f 100644
--- a/test/stack_test.rb
+++ b/test/stack_test.rb
@@ -6,48 +6,43 @@
 describe "Test Stack Implementation" do
   it "creates a Stack" do
     s = Stack.new
-    s.class.must_equal Stack
+    _(s.class).must_equal Stack
   end
 
   it "pushes something onto a empty Stack" do
-    skip
     s = Stack.new
     s.push(10)
-    s.to_s.must_equal "[10]"
+    _(s.to_s).must_equal "[10]"
   end
 
   it "pushes multiple somethings onto a Stack" do
-    skip
     s = Stack.new
     s.push(10)
     s.push(20)
     s.push(30)
-    s.to_s.must_equal "[10, 20, 30]"
+    _(s.to_s).must_equal "[10, 20, 30]"
   end
 
   it "starts the stack empty" do
-    skip
     s = Stack.new
-    s.empty?.must_equal true
+    _(s.empty?).must_equal true
   end
 
   it "removes something from the stack" do
-    skip
     s = Stack.new
     s.push(5)
     removed = s.pop
-    removed.must_equal 5
-    s.empty?.must_equal true
+    _(removed).must_equal 5
+    _(s.empty?).must_equal true
   end
 
   it "removes the right something (LIFO)" do
-    skip
     s = Stack.new
     s.push(5)
     s.push(3)
     s.push(7)
     removed = s.pop
-    removed.must_equal 7
-    s.to_s.must_equal "[5, 3]"
+    _(removed).must_equal 7
+    _(s.to_s).must_equal "[5, 3]"
   end
 end
\ No newline at end of file