If $\displaystyle{\left|{X}\right|}\le{3}\usepackage{cmbright}\Huge\$ , then $\displaystyle-{3}\le{X}\le{3}\usepackage{cmbright}\Huge\$ . In this problem X is $\displaystyle{3}{z}-{9}\usepackage{cmbright}\Huge\$ . This means that you have to solve an inequality with three parts: $\displaystyle-{3}\le{3}{z}-{9}\le{3}\usepackage{cmbright}\Huge\$ . It seems that you only found the solution to $\displaystyle{3}{z}-{9}\le{3}\usepackage{cmbright}\Huge\$ .