Answer:
The constant of proportionality for the group of boxes is: 25
Step-by-step explanation:
Proportion means that change in one quantity causes change in other quantity. Direct variation means that increase in one quantity causes increase in the other quantity.
Let l be the length and v be the volume
Then according to given statement
V∝l
Removing the proportionality symbol introduces a constant in the equation

Putting V = 325 and l = 13

Hence,
The constant of proportionality for the group of boxes is: 25