Answer:
V ∝ a
Explanation:
Let's call each edge length as
.
By definition, we know that the volume of a cube is

Through this expression, you can deduct that the volume of the cube is directly proportional to its edge, that means the volume depends totally on the edge length. A direct proportion means that if the length of the edge increases, then the volume will also increase. This proportion is written like this
V ∝ a
This expression represent all we said before, the volume is directly proportional to its edge length.