Chapter 1, Equations and Inequalities - 1.7 Solve Absolute Value Equations and Inequalities - 1.7 Exercises - Skill Practice - Page 56: 62

$n\geq40$ or $n\leq0$

$|0.4n-8|+4\geq12\\|0.4n-8|\geq8$ implies $0.4n-8\geq8\\0.4n\geq16\\n\geq40$ or $0.4n-8\leq-8\\0.4n\leq0\\n\leq0$. Thus $n\geq40$ or $n\leq0$. Then, by using a graphing utility, the solution set is attached.