You may have correctly simplified this to $\displaystyle-{\left|{b}+{4}\right|}={11}\usepackage{cmbright}\Huge\$ , but then treated it as if it were $\displaystyle{\left|-{b}+{4}\right|}={11}\usepackage{cmbright}\Huge\$ , solving $\displaystyle-{b}+{4}={11}\usepackage{cmbright}\Huge\$ or $\displaystyle-{b}+{4}=-{11}\usepackage{cmbright}\Huge\$ . The correct way to simplify would be $\displaystyle{\left|{b}+{4}\right|}=-{11}\usepackage{cmbright}\Huge\$ .