Answer:
They washed 13 trucks.
Explanation:
This question is solved using a system of equations.
I am going to say that
x is the number of trucks washed
y is the number of cars washed.
The number of trucks washed was 5 fewer than twice the number of cars washed.
This means that
They washed a total of 34 trucks and cars
This means that
How many trucks did they wash?
This is y.
Since
They washed 13 trucks.