\(3\left|x-2\right|-\left|-9\right|=12\\ 3\left|x-2\right|-9=12\\ 3\left|x-2\right|=12+9=21\\ \left|x-2\right|=\dfrac{21}{3}=7\)
Suy ra \(x-2=7\) hoặc \(x-2=-7\)
Vậy \(x=9\) hoặc \(x=-5\)
\(6\left(x-2\right)-\left(x-3\right)=31\\ 6x-12-x+3=31\\ 5x-9=31\\ 5x=31+9=40\\ x=\dfrac{40}{5}=8\)
Vậy \(x=8\)