You may have multiplied 4 feet by $\displaystyle\frac{{{1}\ \text{ foot}}}{{{12}\ \text{ inches}}}\usepackage{cmbright}\Huge\$ . You should multiply 4 feet by $\displaystyle\frac{{{12}\ \text{ inches}}}{{{1}\ \text{ foot}}}\usepackage{cmbright}\Huge\$ .