The rule for rewriting rational exponents is: $\displaystyle{{x}}^{{\frac{{m}}{{n}}}}={\sqrt[{{n}}]{{{{x}}^{{m}}}}}\usepackage{cmbright}\Huge\$

The denominator of the fraction is 3 so this denominator becomes a third root. Because there are no parentheses, the exponent refers only to the quantity immediately to its left.

$\displaystyle{7}{{x}}^{{\frac{{4}}{{3}}}}={7}\cdot{{x}}^{{\frac{{4}}{{3}}}}={7}{\sqrt[{{3}}]{{{{x}}^{{4}}}}}\usepackage{cmbright}\Huge\$