Chapter 1, Equations and Inequalities - 1.7 Solve Absolute Value Equations and Inequalities - 1.7 Exercises - Skill Practice - Page 55: 20

$$r=-8\quad \mathrm{or}\quad \:r=0$$

Since the value inside the absolute value can be positive or negative and get the same number, we must consider both options. Doing this, we find: $$-4-r=-4\quad \mathrm{or}\quad \:-4-r=4 \\ r=-8\quad \mathrm{or}\quad \:r=0$$