How do I solve a1/2(a2/3 -2a1/2)

i assume what you mean to write is:
a^{\frac 1 2}\left(a^{\frac 2 3}-2a^{\frac 1 2}\right)

The problem is that we can't solve this because it is not an equation. You're missing the =. Please add that and any attempts you've made to solve it and we can try again to help you.

Now, you could simplify, but you can't solve.