First, you treated this as an addition problem. You added $\displaystyle-{3}\usepackage{cmbright}\Huge\$ and $\displaystyle-{7}\usepackage{cmbright}\Huge\$ . Then you tried to add $\displaystyle-{6}{{g}}^{{2}}\usepackage{cmbright}\Huge\$ and $\displaystyle{4}{g{}}\usepackage{cmbright}\Huge\$ , but these are unlike terms and cannot be combined. You should add $\displaystyle{\left(-{6}{{g}}^{{2}}+{11}{g{-}}{3}\right)}+{\left(-{4}{g{+}}{7}\right)}\usepackage{cmbright}\Huge\$ . Then regroup and combine like terms. The correct answer is $\displaystyle-{6}{{g}}^{{2}}+{7}{g{+}}{4}\usepackage{cmbright}\Huge\$ .