Answer
$C$
Work Step by Step
We are asked to solve the formula for $h$. First, we want to subtract $2\pi r^2$ from each side of the equation:
$S - 2\pi r^2=2\pi rh $
Divide both sides by $2\pi r$ to isolate $h$:
$\dfrac{S}{2\pi r} - \dfrac{2\pi r^2}{2\pi r}=\dfrac{2\pi rh}{2\pi r} $
Cancel common terms in the numerators and denominators:
$\dfrac{S}{2\pi r} - r=h$
This corresponds to option $C$.
