A clothing business finds there is a linear relationship between the number of shirts, n ,it can sell and the price, p , it can charge per shirt. In particular, historical data shows that 5000 shirts can be sold at a price of $ 72 , while 10000 shirts can be sold at a price of $ 42 . Give a linear equation in the form p = m n + b that gives the price p they can charge for n shirts. p =