Incorrect. Notice that $\displaystyle{{64}}^{{\frac{{1}}{{3}}}}={4}\usepackage{cmbright}\Huge\$ , since $\displaystyle{{4}}^{{3}}={64}\usepackage{cmbright}\Huge\$ . Use the fact that $\displaystyle{{64}}^{{\frac{{2}}{{3}}}}={{\left({{64}}^{{\frac{{1}}{{3}}}}\right)}}^{{2}}\usepackage{cmbright}\Huge\$ to simplify the expression.