Chapter 1, Equations and Inequalities - 1.7 Solve Absolute Value Equations and Inequalities - 1.7 Exercises - Skill Practice - Page 55: 15

$$k=-9\quad \mathrm{or}\quad \:k=3$$

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: $$k+3=-6\quad \mathrm{or}\quad \:k+3=6 \\ k=-9\quad \mathrm{or}\quad \:k=3$$