How do you simplify (216r^9)^(1/3)?

$6 {r}^{3}$
${\left(216 {r}^{9}\right)}^{\frac{1}{3}} = {\left({6}^{3} \cdot {r}^{9}\right)}^{\frac{1}{3}}$
Recall that ${\left({a}^{m}\right)}^{n} = {a}^{m \times n}$
Thus ${\left({6}^{3} \cdot {r}^{9}\right)}^{\frac{1}{3}} = {6}^{\frac{3}{3}} \cdot {r}^{\frac{9}{3}} = 6 {r}^{3}$