Chapter 1, Equations and Inequalities - 1.7 Solve Absolute Value Equations and Inequalities - 1.7 Exercises - Skill Practice - Page 55: 24

$$p=-5\quad \mathrm{or}\quad \:p=9$$

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: $$3p-6=-21\quad \mathrm{or}\quad \:3p-6=21 \\ p=-5\quad \mathrm{or}\quad \:p=9$$