$\displaystyle{2}{x}\usepackage{cmbright}\Huge\$ is a common factor of $\displaystyle{18}{{x}}^{{2}}\usepackage{cmbright}\Huge\$ and $\displaystyle{24}{x}{y}\usepackage{cmbright}\Huge\$ , but it's not the greatest common factor. What is the greatest common factor of 18 and 24?