I'm working through my exercise book quite happily finding indefinite integrals using the table of indefinite integrals, I have come across this one and have been staring at it for an hour unable to understand how this answer is derived.

$\displaystyle

\int \frac{-6}{x^4} dx

$

I know the answer is

$\displaystyle

\frac{2}{x^3} +c

$