Solve
(x^3 y)^2/8x^1/3
Solving implies that you have an equation.
You don't have one.
If you mean simplify ....
(x^3 y)^2 /(8x^(1/3)) , notice I put brackets in so it makes sense
= x^6 y^2 / 2x^(1/3)
= (1/2) x^(17/3) y^2
(certainly does not "look" any more simplified)