|3x+9|<15−x−(15−x)<3x+9<15−x−15+x<3x+92x>−24x>−123x+9<15−x4x<6x<112−12<x<112{\displaystyle {\begin{aligned}&|3x+9|<15-x\\&-(15-x)<3x+9<15-x\\&\color {blue}-15+x<3x+9\\&\color {blue}2x>-24\\&\color {blue}x>-12\\&\color {red}3x+9<15-x\\&\color {red}4x<6\\&\color {red}x<1{\frac {1}{2}}\\&\color {Violet}-12<x<1{\frac {1}{2}}\\\end{aligned}}}