Chapter 1 - Expressions, Equations, and Inequalities - 1-4 Solving Equations - Practice and Problem-Solving Exercises - Page 31: 48

$h=\frac{S}{2 \pi r}-r$

We start by factoring $2\pi r$ out of the right side. We have $2\pi r^2+2\pi rh=2\pi r(r+h)$. Now we divide both sides by $2 \pi r$ to get $\frac{S}{2 \pi r}=r+h$. Finally, to isolate h, we subtract r from both sides to get $\frac{S}{2 \pi r}-r=h$.