Inverse function evaluation 

The derivative of $f(x)=x^5+x^3+x$ is $f'(x) = 5x^4 + 3x^2 + 1$ which is strictly positive.

This means there is only one inverse element $f^{-1}(x)$, i.e, the inverse function is well defined.

By simple inspection we notice that $f(1)=3$, so $f^{-1}(3)=1$. 

One can always guarantee that $f(f^{-1}(2))=2$.