Solve the Equation $$r ^ { 3 } = 36 r$$

Solve the equation. $$r ^ { 3 } = 36 r$$

A) $r = 0 ; r = 6$
B) $r = 0 ; r = 36$
C) $r = 0 ; r = 6 ; r = - 6$
D) $r = 6 ; r = - 6$