I'm not sure what I did wrong here..

$\displaystyle \int 60x \sqrt {1+x} dx$

$\displaystyle u= \sqrt {1+x} $

$\displaystyle x= u^2-1 $

$\displaystyle dx= 2u du $

Then I got

$\displaystyle 60 \int (u^3-u) 2u du $

After I integrated I got

$\displaystyle 120 (\frac {1} {5} u^5- \frac {1} {3} u^3) $

which isn't one of the answer choices...