Brandon bought a new pair of shorts at the store when they were having a 10% off sale. if the regular price of the pair of shorts was $21 how much did brandon pay with the discount?

You would multiply the orignial price by (10%) converted to decimal to find the discount:
21 * 0.10
=2.10

Then, you subract the discount from the original price to see how much he paid:

21 - 2.10 = $18.90

The answer would be $18.90 and the way to find that is you would divide 21 by 100 then multiply it my ten then subtract $2.10 from $21 because $2.10 is 10%. and you would get the final answer $18.90