Integration by substitution

Hi there. I'm new here :-)

I've been going through a fair few substitution questions, but I have been stumped on this one.

I have to solve the following by substitution:

$\displaystyle

\int \sqrt{x^3+1} * x^5 dx$

Now normally I find these questions relatively easy, where all the values under the square root are substituted for u.

This question does not seem to work the same way since $\displaystyle du = 3x^2 dx$ or $\displaystyle x^2=du/3$

Clearly this will not replace the$\displaystyle x^5$ term outside the square root.

Any ideas? :-)