[SOLVED] Surface Area - check my work?

Find the area of the surface obtained by rotating the following curve about the x-axis:

$\displaystyle y = x^3$, $\displaystyle 0 \leq x \leq 3$

Here is my work, which I'm pretty sure is correct, but wrong in Webassign:

$\displaystyle 2\pi \int\limits^{3}_{0} (x^3) \sqrt{1+9x^4} dx$

$\displaystyle \frac{\pi}{18} \int\limits^{729}_{1} \sqrt{u} du$

$\displaystyle = \frac{\pi}{18} \biggl[\frac{2}{3} u^{\frac{3}{2}} \biggr]^{729}_{1}$

$\displaystyle = \frac{\pi}{27} \biggl[729^{\frac{3}{2}} - 1 \biggr]$

Can someone please check my work and let me know where the error is?

Thanks!! Molly