diff --git a/src/objects.ts b/src/objects.ts
index ef6298f..dd25586 100644
--- a/src/objects.ts
+++ b/src/objects.ts
@@ -1,9 +1,9 @@
 // don't change this interface
 interface Book {
   title: string;
-  author: string | string[];
+  author?: string | string[];
   publishedYear: number;
-  genre: string;
+  genre?: string;
   pageCount?: number;
   ISBN?: string;
 }
@@ -27,8 +27,13 @@ function createBook(
   genre: string
 ): Book {
   // write your code here...
-
-  return {} as Book; // replace "{} as Book" with what you see is fit
+  const firstBook: Book = {
+    title,
+    author,
+    publishedYear,
+    genre,
+  };
+  return firstBook; // replace "{} as Book" with what you see is fit
 }
 
 // DO NOT CHANGE THE LINE OF CODE BELOW (you can use it for testing your code)
@@ -50,8 +55,11 @@ const book = createBook(
  */
 function printBookTitleAndYear(book: Book): string {
   // write your code here...
-
-  return ""; // replace empty string with what you see is fit
+  // const theBook: Book = {
+  //   title: "The Book",
+  //   publishedYear: 1965,
+  // };
+  return `${book.title}, ${book["publishedYear"]}`; // replace empty string with what you see is fit
 }
 
 /**
@@ -66,7 +74,7 @@ function printBookTitleAndYear(book: Book): string {
  */
 function addPageCount(book: Book, pageCount: number): Book {
   // write your code here...
-
+  book.pageCount = pageCount;
   return book;
 }
 
@@ -88,7 +96,7 @@ function addPageCount(book: Book, pageCount: number): Book {
  */
 function addISBN(book: Book, ISBN: string): Book {
   // write your code here...
-
+  book.ISBN = ISBN;
   return book;
 }
 
@@ -110,7 +118,7 @@ function addISBN(book: Book, ISBN: string): Book {
  */
 function updatePublishedYear(book: Book, newYear: number): Book {
   // write your code here...
-
+  book.publishedYear = newYear;
   return book;
 }
 
@@ -135,6 +143,13 @@ function updatePublishedYear(book: Book, newYear: number): Book {
  */
 function addSecondAuthor(book: Book, additionalAuthor: string): Book {
   // write your code here...
+  if (Array.isArray(book.author)) {
+    book.author.push(additionalAuthor);
+  } else {
+    book.author = book.author
+      ? [book.author, additionalAuthor]
+      : [additionalAuthor];
+  }
 
   return book;
 }