Inverse variation or direct or neither?

[woof123]

the volume of a sphere: V=(4/3)pi*r³

To me it looks like it is direct variation with a power function (V/r³=(4/3)*pi)but i don't think that's what they're looking for

 

[Deveno]

Strictly speaking, neither, as $V$ does not vary directly with $r$.

It does, however, vary directly with $r^3$, as $\dfrac{4}{3}\pi$ is a constant.