You may have simplified by subtracting the coefficients and then simplified $\displaystyle\sqrt{{{96}{{x}}^{{7}}}}\usepackage{cmbright}\Huge\$ correctly. Rewrite using $\displaystyle\frac{\sqrt{{a}}}{\sqrt{{b}}}=\sqrt{{\frac{{a}}{{b}}}}\usepackage{cmbright}\Huge\$ and simplify by identifying similar factors in the numerator and denominator. Be sure to divide the coefficients and subtract the exponents. Identify perfect squares and pull them out of the radical. The correct answer is $\displaystyle{7}{{x}}^{{3}}\sqrt{{{x}}}\usepackage{cmbright}\Huge\$ .