A contractor needs to buy nails to build a house. The nails come in small boxes and large boxes. Each small box has 200 nails and each large box has 400 nails. The contractor bought twice as many small boxes as large boxes, which altogether had 3200 nails. Graphically solve a system of equations in order to determine the number of small boxes purchased, x, x, and the number of large boxes purchased, yy.