Interval Notation: $(-\infty, 0]$ Refer to the image below for the graph.
Work Step by Step
The solution set of the given inequality includes all the numbers that are less than or equal to $0$. The set includes all the numbers to the left of $0$ so $-\infty$ will be used on the left side of the interval notation. The highest number in the set is $0$ so a bracket will be used on the right side of the interval. Thus, the interval notation equivalent of the given inequality is: $(-\infty, 0]$. To graph the solution set on a number line, plot a solid dot at $x=0$ then shade the region to its left. (refer to the attached image in the answer part above)