If you want to find a discount, multiply the values together.
180*0.15 = 27.
180-27 = 153.
At Sport City, the discounted tennis racket is $153.
200*0.2 = 40.
200-40 = 160.
At Tennis World, the discounted tennis racket is $160.
$153 < $160, so Sport City has the better deal.
Hope that helped you.