Cars and trucks are the most popular vehicles. last year, the number of cars sold was 39,000 more than 3 times the number of trucks sold. There were 216,000 cars sold last year. Write an equation that can be used to find the number of trucks, t, sold last year.

Let c be the number of cars.
Let t be the number of trucks.

We're given two equations:

c = 3t + 39000

c + t = 216000

Substitute equation (1) into equation (2) for c:
3t + 39000 + t = 216000