First tell the matter to ur class teacher. Then ask the whole class if anyone had seen tje book lying here or there. If u r not able to find the book ti now, then go to the librarian and talk to her abjout the issue and take her suggestions. If it is not at all possible to find the book now then either u pay the whole amount of money to the librarian or u must buy that very book from the market and hand it over to the librarian directly.