Precalculus (6th Edition) Blitzer

Step 1. Graph the line $y=\frac{1}{3}x$; as the inequality includes an equal sign, make this line solid. Step 2. Using a test point away from the line, such as $(3,0)$, we have $0\lt1$ which satisfies the inequality; thus the side with this test point should be shaded as shown in the figure.