Let $f$: $\mathbb{R}$ to $\mathbb{R}$ defined by $f(x) = x^3+x^2$. Prove that $f(x)$ is a surjective function.

I'm not quite sure how to approach this problem. If the function had an inverse, I could show that it would be bijective and therefore surjective, but this function does not have an inverse.

I was given the hint to use the Intermediate Value Theorem, but I don't see how this would help on the interval (-1, 0).

Any assistance is greatly appreciated.