Answer:
it's almost $100 and there's $17 off. so 99.99-17 would make the exact cost 82.99
82.99/99.99= 0.8299 so you payed 83% and that would make it so you got a 17% discount.
but if you didn't want to do all the math, you could've just rounded the 99.99 up to 100, and $17 would make it a 17% discount.