Answer
$x^2 -2x - 15 \leq0$.
Work Step by Step
To answer this exercise, it helps to first write the interval as individual values of $x$, which is to say, $x \geq -3$ and $x \leq 5$. If we were to draw their number lines, we would see that, in order for both inequalities to be a part of a polynomial inequality, we would require their multiplication to be negative, which results in $(x+3)(x-5) \leq 0$, also written as $x^2 -2x - 15 \leq0$.
