An invoice clerk receives a bill for RM 37.50 for ten blank ledger books and three special filling trays. On phoning the supplier (after discovering the order had been written out incorrectly) the clerk agrees to return three of the ledger books in return for the supplier sending an extra filling tray. Given that there will be an extra RM 2.50 to pay and there is a 10% discount for orders of 10 ledger books or more. Find the price of a single ledger book and a filling tray.​