Add 9 to both sides of the inequality: $\displaystyle{3}{\left|{m}+{7}\right|}<{39}\usepackage{cmbright}\Huge\$

Divide both sides by 3: $\displaystyle{\left|{m}+{7}\right|}<{13}\usepackage{cmbright}\Huge\$

Rewrite without absolute value: $\displaystyle-{13}<{m}+{7}<{13}\usepackage{cmbright}\Huge\$

Subtract 7 from all 3 parts: $\displaystyle-{20}<{m}<{6}\usepackage{cmbright}\Huge\$