Correct. $\displaystyle{a}={0}\usepackage{cmbright}\Huge\$ must be excluded from the domain since $\displaystyle\frac{{15}}{{{\left({0}\right)}}^{{3}}}\usepackage{cmbright}\Huge\$ is undefined. Simplifying this expression you find that $\displaystyle\frac{{{12}{{a}}^{{2}}}}{{5}}\cdot\frac{{15}}{{{a}}^{{3}}}=\frac{{36}}{{a}}\usepackage{cmbright}\Huge\$ .