#### Answer

$f'(x) = (336x^{3})(3x^4+2)^{-5}$

#### Work Step by Step

In order to derivate this function you have to apply the chain rule
Let's make an «u» substitution to make it easier
$u = 3x^4+2 $
$f(u) = -7u^{-4}$
Derivate the function:
$f'(u) = 28u^{-5}u'$
Now let's find u'
$u' = 12x^{3}$
Then undo the substitution, simplify and get the answer:
$f'(x) = 28(12x^{3})(3x^4+2)^{-5}$
$f'(x) = (336x^{3})(3x^4+2)^{-5}$