Start with $\displaystyle{13.1}-{20.2}={13.1}+{\left(-{20.2}\right)}\usepackage{cmbright}\Huge\$ . Since $\displaystyle{20.2}-{13.1}={7.1}\usepackage{cmbright}\Huge\$ , and $\displaystyle{20.2}>{13.1}\usepackage{cmbright}\Huge\$ , $\displaystyle{13.1}+{\left(-{20.2}\right)}=-{7.1}\usepackage{cmbright}\Huge\$ . Then add 9 to get $\displaystyle{1.9}\usepackage{cmbright}\Huge\$ . Finally, rewrite $\displaystyle{1.9}-{\left(-{38.5}\right)}\usepackage{cmbright}\Huge\$ as $\displaystyle{1.9}+{38.5}\usepackage{cmbright}\Huge\$ to get 40.4.