It appears that you mistakenly applied the exponent $\displaystyle\frac{{1}}{{3}}\usepackage{cmbright}\Huge\$ in the denominator to the factor $\displaystyle{{m}}^{{2}}\usepackage{cmbright}\Huge\$ , even though it was not inside the parentheses. The denominator should be rewritten as: $\displaystyle{{m}}^{{2}}\cdot{{125}}^{{\frac{{1}}{{3}}}}\cdot{{n}}^{{\frac{{1}}{{3}}}}={{m}}^{{2}}\cdot{5}\cdot{{n}}^{{\frac{{1}}{{3}}}}\usepackage{cmbright}\Huge\$