Chapter 1, Equations and Inequalities - 1.7 Solve Absolute Value Equations and Inequalities - 1.7 Exercises - Skill Practice - Page 55: 12

$$f=2\quad \mathrm{or}\quad \:f=8$$

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: $$\left|f-5\right|=3 \\ f-5=-3\quad \mathrm{or}\quad \:f-5=3 \\ f=2\quad \mathrm{or}\quad \:f=8$$