Answer:
3 groups of 21 cars and 4 groups of 21 trucks
Explanation:
In this case, what we must do is find the largest common divisor since this would be the answer to the question. So:
LCD (63, 84), in this case it is 21.
63/21 = 3
84/21 = 4
He could have 3 groups of 21 cars and 4 groups of 21 trucks.