Mr.Brown is throwing the entire class a pizza party (not really, keep reading)! When he places the order from Tony's pizza across the street, he learns that each medium pizza has 6 slices, and each large pizza has 8 slices. If Mr.Brown orders 9 total pizzas with a total of 66 slices, how many of each size pizza did he buy? Let x represent the number of medium pieces and let y represent the number of large pizzas.