Answer
$(-\infty, -4]\cup[0,4]$
Work Step by Step
Step 1. Factor the inequality to get $x(x+4)(x-4)\leq0$
Step 2. Identify the boundary points $x=-4, 0, 4$ and separate the number line into intervals $(-\infty, -4)$, $(-4,0)$, $(0,4)$ and $(4,\infty)$
Step 3. Use test points $x=-5,-1,1,5$ to get the signs of the left side of the inequality as $-,+,-,+$
Step 4. Based on the signs and consider the boundary points for the equal sign, we have the solution as $(-\infty, -4]\cup[0,4]$