A new clothing store is offering 30 free points to customers who sign up for their rewards card. Then for each shirt a customer buys, they earn an additional number of points. Mr. Smith signs up for the rewards card and purchases 3 shirts. He earns 75 points. How many additional points does a customer earn on purchasing one shirt? Write an equation that represents the relationship between the number of shirts purchased, n, and the total number of points earned, p.
[latex]p=45 \ n=3 \ 45/3=15[/latex] for every shirt a customer buys they recieve 15 points