Answer
$8x^{5/12}$
Work Step by Step
$\displaystyle \frac{72x^{3/4}}{9x^{1/3}}=\frac{72}{9}\cdot\frac{x^{3/4}}{x^{1/3}}\qquad$... apply $\displaystyle \frac{a^{m}}{a^{n}}=a^{m-n}$
$=8\cdot x^{3/4-1/3}\qquad$...$\displaystyle \frac{3}{4}-\frac{1}{3}=\frac{9-4}{12}$ ...
$=8x^{5/12}$
