Answer:
2.5-ton payload per truck
Explanation:
Given the following equation:
total payload = 2.5-ton payload per truck * number of trucks
it can be rewritten as:
y = k*x
where y and x are variables and k is the constant of variation. Comparing these two equation, we see that 2.5-ton payload per truck is the constant of variation, and total payload and number of trucks are the directly variated variables, because when the number of trucks increase, the total payload also increased.