diff --git a/Exercises/1-callback.js b/Exercises/1-callback.js
index 8270a12..ccde3b3 100644
--- a/Exercises/1-callback.js
+++ b/Exercises/1-callback.js
@@ -1,5 +1,10 @@
 'use strict';
 
-const iterate = (obj, callback) => null;
+const iterate = (object, callback) => {
+  for (const key in object) {
+    const value = object[key];
+    callback(key, value, object);
+  }
+};
 
 module.exports = { iterate };
diff --git a/Exercises/2-closure.js b/Exercises/2-closure.js
index 0f07103..7b71264 100644
--- a/Exercises/2-closure.js
+++ b/Exercises/2-closure.js
@@ -1,5 +1,5 @@
 'use strict';
 
-const store = x => null;
+const store = x => () => x;
 
 module.exports = { store };
diff --git a/Exercises/3-wrapper.js b/Exercises/3-wrapper.js
index fb7207e..fd1441b 100644
--- a/Exercises/3-wrapper.js
+++ b/Exercises/3-wrapper.js
@@ -1,5 +1,24 @@
 'use strict';
 
-const contract = (fn, ...types) => null;
+const contract = (fn, ...types) => (...args) => {
+  args.forEach((arg, index) => {
+    const typeName = types[index].name.toLowerCase();
+    const argType = typeof arg;
+    if (typeName !== argType) {
+      throw new TypeError(`Argument type expected:
+       ${typeName}, got: ${argType}`);
+    }
+  });
+  const result = fn(...args);
+  const expectedResultType = types[types.length - 1].name.toLowerCase();
+  const resultType = typeof result;
+
+  if (expectedResultType !== resultType) {
+    throw new TypeError(`Result type expected:
+     ${expectedResultType}, got: ${resultType}`);
+  }
+
+  return result;
+};
 
 module.exports = { contract };