First find the total cost of the spellbooks by multiplying the price per book by the number of books: 5 books * 5 gold/book = <<5*5=25>>25 gold
Then add that amount to the cost of the owl: 25 gold + 28 gold = <<25+28=53>>53 gold
Now multiply that number by the conversion rate between gold and silver: 53 gold * 9 silver/gold = <<53*9=477>>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 = <<3*20=60>>60 silver
Now add that amount to the cost of the books and owl to find Harry's total spending: 60 silver + 477 silver = <<60+477=537>>537 silver
#### 537