A clothing business finds there is a linear relationship between the number of shirts,nn,it can sell and the price,pp, it can charge per shirt. In particular, historical data shows that 30003000 shirts can be sold at a price of $70$70, while 2300023000 shirts can be sold at a price of $30$30. Give a linear equation in the form p=mn+bp=mn+b that gives the price pp they can charge for nn shirts.