$\displaystyle-{52.8}-{\left(-{68.9}\right)}=-{52.8}+{68.9}\usepackage{cmbright}\Huge\$ . Now find the difference of the absolute values: $\displaystyle{68.9}-{52.8}={16.1}\usepackage{cmbright}\Huge\$ . Because the addend with the greater absolute value is positive, the answer is positive.