Correct. $\displaystyle\frac{{{12}}}{{x}}+\frac{{{9}{x}}}{{3}}=\frac{{{3}{{x}}^{{2}}+{12}}}{{x}}\usepackage{cmbright}\Huge\$ ; the domain excludes $\displaystyle{x}={0}\usepackage{cmbright}\Huge\$ because $\displaystyle\frac{{12}}{{0}}\usepackage{cmbright}\Huge\$ is undefined.