Question

c. $c = 2pi r$ for $r$

Explanation:

Step1: Isolate $r$ via division

Divide both sides by $2\pi$.
$\frac{C}{2\pi} = \frac{2\pi r}{2\pi}$

Step2: Simplify the right-hand side

Cancel $2\pi$ terms on the right.
$\frac{C}{2\pi} = r$

Answer:

$r = \frac{C}{2\pi}$