You may have incorrectly added $\displaystyle-{30}+{\left(-{15}\right)}\usepackage{cmbright}\Huge\$ to get $\displaystyle-{15}\usepackage{cmbright}\Huge\$ , and then incorrectly added $\displaystyle-{15}+{80}\usepackage{cmbright}\Huge\$ . To add two negative numbers, you must add their absolute values ( $\displaystyle{30}+{15}\usepackage{cmbright}\Huge\$ ), and place a negative sign on the result ( $\displaystyle-{45}\usepackage{cmbright}\Huge\$ ). To add $\displaystyle-{45}\usepackage{cmbright}\Huge\$ and 80, find the difference of their absolute values. Since $\displaystyle{\left|{80}\right|}>{\left|-{45}\right|}\usepackage{cmbright}\Huge\$ , the result will be positive.