Answer :

[tex]|x-18|\geq6\iff x-18\geq6\ \vee\ x-18\leq-6\ \ \ |add\ 18\ to\ both\ sides\\\\x\geq24\ \vee\ x\leq12\\\\x\in(-\infty;12]\ \cup\ [24;\ \infty)[/tex]
[tex]|x-18|\geq6\\ x-18\geq 6 \vee x-18\leq-6\\ x\geq24 \vee x\leq 12\\ x\in(-\infty,12\rangle\cup\langle24,\infty)[/tex]