Factorize the numerator!
By grouping we get
This should get you started. Note the 2nd factor is the difference of cubes and can be factored as well.
after you have factored both the numerator and denominator the entire denominator should reduce out.
Try to work this out and post back with your work if you get stuck.
You can almost do this "by inspection".
I see , so I see an in there.
The rest of the numerator is , which factors into .
I don't suppose you tried long division . . .