The correct graph is the third one, with the solid dots at -3 and 3.
The bars around x stand for absolute value, which is defined as the distance a number is from 0. We want to know what number or numbers is/are 3 units away from 0 on a number line; the only choices are 3 or -3.
This means we must plot points at -3 and 3. They must be solid points, since these numbers are included in the solution (they are, in fact, the only ones of the solution).