You may have subtracted $\displaystyle\frac{{2}}{{3}}-\frac{{1}}{{4}}\usepackage{cmbright}\Huge\$ . You need to regroup $\displaystyle{3}\frac{{1}}{{4}}\usepackage{cmbright}\Huge\$ or rewrite it as an improper fraction, find a common denominator, and then subtract $\displaystyle{2}\frac{{1}}{{3}}\usepackage{cmbright}\Huge\$ .