You may have forgotten to change the direction of the inequality symbol after you divided both sides by $\displaystyle-{6}\usepackage{cmbright}\Huge\$ . The solution to this inequality is $\displaystyle{b}<-{3}\usepackage{cmbright}\Huge\$ , while the graph shown represents $\displaystyle{b}>-{3}\usepackage{cmbright}\Huge\$ .