Answer
$(-\infty,4]$
Work Step by Step
Step 1. Factor the inequality as $x^2(x-4)\leq0$. Then the boundary points are $x=0,4$
Step 2. Using the test points to examine signs across the boundary points, we have
$...(-)...(0) ...(-)...(4)...(+)...$
Thus the solutions are $x\leq4$
Step 3. We can express the solutions on a real number line as shown in the figure.
Step 4. We can express the solutions in interval notation as $(-\infty,4]$
