Chapter 1 - 1.7 - Linear Inequalities in One Variable - 1.7 Exercises - Page 137: 49

$x\geq14\text{ and }x\leq26$ See graph

Apply absolute rule: If $|u|\leq a,~a\gt0$, then $-a\leq u\leq a$, Take $u=x-20$ and $a=6$: $$-6\leq x-20\leq6$$ $$x-20\geq-6\text{ and }x-20\leq6$$ $$x-20+20\geq-6+20\text{ and }x-20+20\leq6+20$$ $$x\geq14\text{ and }x\leq26$$ The graph of the solution set is as shown.