Use the inverse variation equation $\displaystyle{y}=\frac{{k}}{{x}}\usepackage{cmbright}\Huge\$ : $\displaystyle{10}=\frac{{k}}{{6}}\usepackage{cmbright}\Huge\$ , so $\displaystyle{k}={60}\usepackage{cmbright}\Huge\$ .

Substitute 12 and 5: $\displaystyle{12}=\frac{{k}}{{5}}\usepackage{cmbright}\Huge\$ also yields $\displaystyle{k}={60}\usepackage{cmbright}\Huge\$ , so this is an inverse relationship.