The original price of a football helmet was $78.60. if peter was given a 15% discount how much did he pay for the football helmet

First you have to find out what one percent of the price is by deviding 78.6 by 100. One percent is 0.786. You want to know what 15 percent of the price is so that you can subtract this as a discount, you do this by multiplying 0.786 by fifteen. That is 11.79 = the discount. Subtract 11,79 from 78.6 and there is your answer.

He payed 66.81 dollars for the football helmet.

Yes the slope to this is -5