You added $\displaystyle-{52.8}\usepackage{cmbright}\Huge\$ and $\displaystyle-{68.9}\usepackage{cmbright}\Huge\$ instead of rewriting the problem as $\displaystyle-{52.8}-{\left(-{68.9}\right)}=-{52.8}+{68.9}\usepackage{cmbright}\Huge\$ . The correct answer is 16.1.