input: Write a python function to find all pages that contain a given book title from a dictionary.
  assert find_pages(page_dict, "The Lord of the Rings")==[1, 32, 54, 75]
  assert find_pages(page_dict, "Harry Potter and the Sorcerer's Stone")==[1, 26, 92, 132]
  assert find_pages(page_dict, "To Kill a Mockingbird")==[1, 15, 52, 101]
output: def find_pages(page_dict, book_title):
      return [page for page, title in page_dict.items() if title == book_title]