I cannot figure out what to do!!

Given the function $\displaystyle f(x)=5 x^3+2 x+5$ Let g be the inverse function of f. i.e. $\displaystyle g(x)=f^{-1}(x).$

$\displaystyle g^{\prime}(12)=$

I can't manage to find g(x) let alone g'(x)

Thank you for any help.