diff --git a/src/challenge.ts b/src/challenge.ts
index d697960..6831415 100644
--- a/src/challenge.ts
+++ b/src/challenge.ts
@@ -38,7 +38,11 @@ function addReview(
   reviewer: string,
   comment: string
 ): ReviewedBook {
-  // write your code here...
+  const newReview: Review = { reviewer, comment };
+  if (!book.reviews) {
+    book.reviews = [];
+  }
+  book.reviews.push(newReview);
 
   return book;
 }
diff --git a/src/objects.ts b/src/objects.ts
index ef6298f..9f3f618 100644
--- a/src/objects.ts
+++ b/src/objects.ts
@@ -26,9 +26,12 @@ function createBook(
   publishedYear: number,
   genre: string
 ): Book {
-  // write your code here...
-
-  return {} as Book; // replace "{} as Book" with what you see is fit
+  return {
+    title,
+    author,
+    publishedYear,
+    genre,
+  };
 }
 
 // DO NOT CHANGE THE LINE OF CODE BELOW (you can use it for testing your code)
@@ -49,9 +52,7 @@ const book = createBook(
  *   // => "Hitchhiker's Guide to The Galaxy 1965"
  */
 function printBookTitleAndYear(book: Book): string {
-  // write your code here...
-
-  return ""; // replace empty string with what you see is fit
+  return book.title + " " + book["publishedYear"];
 }
 
 /**
@@ -65,8 +66,7 @@ function printBookTitleAndYear(book: Book): string {
  *   // => { title: "Hitchhiker's Guide to The Galaxy", author: "Douglas Adams", publishedYear: 1965, genre: "Sci-Fi", pageCount: 320 }
  */
 function addPageCount(book: Book, pageCount: number): Book {
-  // write your code here...
-
+  book.pageCount = pageCount;
   return book;
 }
 
@@ -87,8 +87,7 @@ function addPageCount(book: Book, pageCount: number): Book {
  *   //    }
  */
 function addISBN(book: Book, ISBN: string): Book {
-  // write your code here...
-
+  book.ISBN = ISBN;
   return book;
 }
 
@@ -109,7 +108,7 @@ function addISBN(book: Book, ISBN: string): Book {
  *   //    }
  */
 function updatePublishedYear(book: Book, newYear: number): Book {
-  // write your code here...
+  book.publishedYear = newYear;
 
   return book;
 }
@@ -134,8 +133,11 @@ function updatePublishedYear(book: Book, newYear: number): Book {
  *   //    }
  */
 function addSecondAuthor(book: Book, additionalAuthor: string): Book {
-  // write your code here...
-
+  if (typeof book.author === "string") {
+    book.author = [book.author, additionalAuthor];
+  } else {
+    book.author.push(additionalAuthor);
+  }
   return book;
 }