Consider the question. Harry needs to buy 5 spellbooks that each cost 5 gold, three potion kits that each cost 20 silver, and one owl that costs 28 gold. There are 9 silver to a gold. How much will Harry pay total, in silvers?
 If the answer is '537'; explain the reasoning:
First find the total cost of the spellbooks by multiplying the price per book by the number of books: 5 books * 5 gold / book = 25 gold. Then add that amount to the cost of the owl: 25 gold + 28 gold = 53 gold. Now multiply that number by the conversion rate between gold and silver: 53 gold * 9 silver / gold = 477 silver. Now find the total cost of the potion kits by multiplying the price per kit by the number of kit: 3 kits * 20 silver / kit = 60 silver. Now add that amount to the cost of the books and owl to find Harry's total spending: 60 silver + 477 silver = 537 silver.