A contractor needs to buy nails to build a house. The nails come in small boxes and large boxes. Each small box has 50 nails and each large box has 350 nails. The contractor bought 3 more small boxes than large boxes, which altogether had 2950 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.

Let's define the variables:

Let "s" represent the number of small boxes purchased.
Let "l" represent the number of large boxes purchased.

With these variables defined, we can write the system of equations as follows:

Equation 1: s = l + 3 (The contractor bought 3 more small boxes than large boxes)

Equation 2: 50s + 350l = 2950 (The total number of nails purchased is equal to 2950)

And there you have it, the system of equations to determine the number of small boxes and large boxes purchased.