How to solve $x^{2/3}=4$?

This is still a hint

$$x^{2/3}=4$$ $$x^{2}=4^3=64$$

$$x=\pm8$$

I leave the rest to you!

You multiply both sides by $3$, getting $x^2=12$. Can you take it from here? Note that x^2/3 usually means $(x^2)/3$, not $x^{(2/3)}$