Find all the real zeros of the polynomial $$P(x)=x^4 - x^3 - 16 x^2 + 16 x .$$
Its real zeros are $x_1=$ , $x_2=$ , $x_3=$ and $x_4=$ with $x_1\le x_2\le x_3\le x_4$.
Note: If the polynomial has only three real zeros, input them at $x_1$, $x_2$ and $x_3$; if the polynomial has only two real zeros, input them at $x_1$ and $x_2$; if the polynomial has only one real zero, input it at $x_1$. Give EXACT answers. No decimals.

When $x\to\infty$, $P(x)\to$
When $x\to-\infty$, $P(x)\to$
If your answer is $\infty$, enter infinity; if your answer is $-\infty$, enter -infinity.