You may have thought the starting temperature was $\displaystyle-{{9}}^{\circ}\text{C}\usepackage{cmbright}\Huge\$ instead of $\displaystyle{{9}}^{\circ}\text{C}\usepackage{cmbright}\Huge\$ . The problem is asking you to find $\displaystyle{9}-{23}\usepackage{cmbright}\Huge\$ .