You may have thought the starting temperature was $\displaystyle-{{7}}^{\circ}\text{F}\usepackage{cmbright}\Huge\$ instead of $\displaystyle{{7}}^{\circ}\text{F}\usepackage{cmbright}\Huge\$ . The problem asks you to find $\displaystyle{7}-{30}\usepackage{cmbright}\Huge\$ .