recall that for a cube, all dimensions, length, width and height, are the same in value.
so, if say length = width = height = x, then the volume of the cube is V = x³, therefore
[tex]\bf V=x^3\implies \cfrac{dV}{dt}=\stackrel{chain~rule}{3x^2\cfrac{dx}{dt}}\quad
\begin{cases}
x=30\\
\frac{dx}{dt}=\stackrel{cm/hr}{2}
\end{cases}\implies \cfrac{dV}{dt}=3(30)^2(2)
\\\\\\
\cfrac{dV}{dt}=5400[/tex]
