1.8: Rate of increase of a cuboid dimension

When poured from a pipe, concrete is formed into the shape of a cuboid with a square base of side $\displaystyle x$ and height $\displaystyle 3x$.

The volume of the cuboid increases at a constant rate of $\displaystyle 8\,\mathrm{m}^3\mathrm{s}^{-1}$.

Find the rate of increase, in $\displaystyle \mathrm{m\,s^{-1}}$, of $\displaystyle x$ when $\displaystyle x=2$ metres.