Two customers went to the post office to buy postcards and large envelopes. Each postcard costs the same amount, and each large envelope costs the same amount. The first customer paid $12 for 14 postcards and 5 large envelopes. The second customer paid $24.80 for 10 postcards and 15 large envelopes. Write a system of equations to model the situation above for x number of postcards and y number of envelopes.