You found an equivalent expression by pulling out $\displaystyle\sqrt{{{9}{{x}}^{{2}}}}\usepackage{cmbright}\Huge\$ from the numerator and $\displaystyle\sqrt{{{4}}}\usepackage{cmbright}\Huge\$ from the denominator, but this expression will simplify further. Start by rewriting $\displaystyle\frac{\sqrt{{{72}{{x}}^{{2}}}}}{\sqrt{{{24}{x}}}}\usepackage{cmbright}\Huge\$ using $\displaystyle\frac{\sqrt{{a}}}{\sqrt{{b}}}=\sqrt{{\frac{{a}}{{b}}}}\usepackage{cmbright}\Huge\$ and simplify the fraction.