You did not follow the laws of exponents, and treated $\displaystyle{{\left({125}{n}\right)}}^{{\frac{{1}}{{3}}}}\usepackage{cmbright}\Huge\$ as if it were $\displaystyle{125}{{n}}^{{\frac{{1}}{{3}}}}\usepackage{cmbright}\Huge\$ . The correct way to apply the exponent would be $\displaystyle{{125}}^{{\frac{{1}}{{3}}}}{{n}}^{{\frac{{1}}{{3}}}}\usepackage{cmbright}\Huge\$ , which simplifies to: $\displaystyle{5}{{n}}^{{\frac{{1}}{{3}}}}\usepackage{cmbright}\Huge\$