A contractor needs to buy nails to build a house. The nails come in small boxes and large boxes. Each small box has 150 nails and each large box has 450 nails. The
contractor bought twice as many large boxes as small boxes, which altogether had
4200 nails. Write a system of equations that could be used to determine the number
of small boxes purchased and the number of large boxes purchased. Define the
variables that you use to write the system.