Solve each of the following geometric formulas for the radius $r$. Enter $\pi$ as pi.

(a) The circumference of a circle of radius $r$ is $C = 2 \pi r$.
$r$ = help (formulas)

(b) The area of a circle of radius $r$ is $A = \pi r^2$.
$r$ = help (formulas)

(c) The volume of a sphere of radius $r$ is $\displaystyle V = \frac{4}{3} \pi r^3$.
$r$ = help (formulas)

(d) The volume of a cylinder of radius $r$ and height $h$ is $V = \pi r^2 h$.
$r$ = help (formulas)

(e) The volume of a cone of radius $r$ and height $h$ is $\displaystyle V = \frac{1}{3} \pi r^2 h$.
$r$ = help (formulas)