You may have misread the graph or incorrectly reversed the inequality sign after division by 4. Reverse the inequality sign only after multiplication or division by a negative number. The solution to this inequality is $\displaystyle{c}\ge{5}\usepackage{cmbright}\Huge\$ , while the graph shown represents $\displaystyle{c}\le{5}\usepackage{cmbright}\Huge\$ . The correct answer is $\displaystyle-{3}{c}\ge-{15}\usepackage{cmbright}\Huge\$ .