You may have partially used the laws of exponents to simplify. However, you incorrectly set the index 3 as the numerator over each of the exponents in the variable terms. The expression can first be rewritten as: $\displaystyle{{\left({27}{{x}}^{{6}}{y}{{z}}^{{3}}\right)}}^{{\frac{{1}}{{3}}}}\usepackage{cmbright}\Huge\$

The second step is to write the expression as: $\displaystyle{{27}}^{{\frac{{1}}{{3}}}}\cdot{{\left({{x}}^{{6}}\right)}}^{{\frac{{1}}{{3}}}}\cdot{{\left({y}\right)}}^{{\frac{{1}}{{3}}}}\cdot{{\left({{z}}^{{3}}\right)}}^{{\frac{{1}}{{3}}}}\usepackage{cmbright}\Huge\$