Write and graph a piecewise function that models the situation and answer the question. A print shop charges $20 to set up the graphic for printing t-shirts. The store then charges $12 per shirt for purchasing up to 10 shirts. The charge decreases to $10 if a customer purchases 10-20 shirts. If a customer purchases more than 20 shirts, each shirt will cost $7. What will it cost a soccer team to have 15 shirts printed?