That depends on what the problem is. You might want to add some parentheses next time.
If you mean:
4x^4 - (x^3)/(8x-2)
4x^4(8x-2)/(8x-2) - (x^3)/(8x-2)
(32x^5 - 8x^4 - x^3)/(8x-2)
(x^3)(32x^2 - 8x -1)/(8x-2)
.
4x^4 - (x^3)/(8x) - 2
4x^4 - (1/8)x^2 - 2
(1/8)(32x^4 - x^2 - 16)