Correct. The value of the denominator is 12, so $\displaystyle{2}{a}={12}\usepackage{cmbright}\Huge\$ , which means $\displaystyle{a}={6}\usepackage{cmbright}\Huge\$ . Using this value for a, you find $\displaystyle{4}{a}{c}={72}\usepackage{cmbright}\Huge\$ , so $\displaystyle{4}{\left({6}\right)}{c}={72}\usepackage{cmbright}\Huge\$ , so $\displaystyle{c}={3}\usepackage{cmbright}\Huge\$ . Finally, $\displaystyle{b}={11}\usepackage{cmbright}\Huge\$ .