Your answer is right, but we need to somehow get x-2 instead of 4x-8:
At the step:
[tex]\frac{(4x-8)(-12x^3) +6x^4}{(4x-8)^{\frac{1}{2}}(4x-8)}[/tex]
We can factor a number out of (4x-8)1/2. We can also factor a number out of (4x-8). Once you get to the last step of your work, you can factor out a number from (14x-32).