What does (x^3 - (3/x))^8 expand to?
Do you know the binomial theorem?
Check out these...
Binomial Theorem Calculator
Pascal's Triangle and the Binomial Expansion ...........................
Via Pascal's triangle your coefficents are $\displaystyle 1,8,28,56,70,56,28,8,1$
Using these the expansion is...
$\displaystyle 1\times (x^3)^8\times \left(\frac{-3}{x}\right)^0+8\times (x^3)^7\times \left(\frac{-3}{x}\right)^1+28\times (x^3)^6\times \left(\frac{-3}{x}\right)^2+\dots
$
Do you see the pattern?