Answer
$h=\frac{A-\pi{r^2}}{2\pi{r}}$
Work Step by Step
Subtract $\pi{r^2}$ to both sides:
$A-\pi{r^2}=2\pi{rh}+\pi{r^2}-\pi{r^2}
\\A-\pi{r^2}=2\pi{rh}$
Divide $2\pi{r}$ to both sides:
$\frac{A-\pi{r^2}}{2\pi{r}}=\frac{2\pi{rh}}{2\pi{r}}
\\\frac{A-\pi{r^2}}{2\pi{r}}=h$
