Incorrect. Use the facts that $\displaystyle{256}={{4}}^{{4}}\usepackage{cmbright}\Huge\$ , $\displaystyle{{256}}^{{-\frac{{3}}{{4}}}}={{\left({{256}}^{{\frac{{1}}{{4}}}}\right)}}^{{-{{3}}}}\usepackage{cmbright}\Huge\$ , and $\displaystyle{{x}}^{{-{{3}}}}=\frac{{1}}{{{{x}}^{{3}}}}\usepackage{cmbright}\Huge\$ .