well, what I did was subbed in the quartic function for 'u' and then applied the chain rule to the first part, and I expanded the second part out, and took its derivative. Now that gets me something messy. The answer in the back gives me some silly answer that has a 'u' and an 'x' in it. (3u^2+6)(8x^3+6x)
Makes no sense to me.