Question 544257
This can be solved by setting up a system of equations with two equations and two variables. The variables, c and v, represent the number of cars and vans respectively. The equations are just the sum of $200 by adding $3 for every car plus $5 for every van, and the conversion of thrice as many cars to vans:

3c + 5v >= 200
c = 3v

Now you can solve because remember if you have as many equations as you do variables, you can solve for all variables. Just use the substitution method:

3(3v) + 5v >= 200
9v + 5v >= 200
14v >= 200
÷ 14 = ÷ 14
v >= 14 2/7
So v = 15, since they must've washed a whole number of vans. The number of cars is 3 times this amount or 15 * 3 = 45. Therefore they washed 45 cars and 15 vans to reach their goal. You can check your answer:
3*45 + 5*15 >= 200