input: Write a function to create a Book object and return its string representation.
  assert str(create_book("The Great Gatsby", "F. Scott Fitzgerald", 180)) == "Book: The Great Gatsby, by F. Scott Fitzgerald (180 pages)"
  assert str(create_book("To Kill a Mockingbird", "Harper Lee", 281)) == "Book: To Kill a Mockingbird, by Harper Lee (281 pages)"
  assert str(create_book("1984", "George Orwell", 328)) == "Book: 1984, by George Orwell (328 pages)"
output: def create_book(title, author, pages):
      class Book:
          def __init__(self, title, author, pages):
              self.title = title
              self.author = author
              self.pages = pages
          
          def __str__(self):
              return f"Book: {self.title}, by {self.author} ({self.pages} pages)"
      
      return Book(title, author, pages)