Having a bit of trouble with this one. Can anyone help?

Many thanks.The surface are, S, of a cylinder is given by S = 2$\displaystyle \pi$r

Q.^{2}+ 2$\displaystyle \pi$rh. Its volume, V, is given by V = $\displaystyle \pi$r^{2}h. Express V in terms of S & r only.

Attempt:V = S => $\displaystyle \pi$r^{2}h = 2$\displaystyle \pi$r^{2}+ 2$\displaystyle \pi$rh => $\displaystyle \pi$r^{2}h = 2$\displaystyle \pi$(r^{2}+ rh) => V = ...

Ans.:V = $\displaystyle \frac{r}{2}$(S - 2$\displaystyle \pi$r^{2})