You may have used an equation for direct variation, such as $\displaystyle{x}={k}{y}\usepackage{cmbright}\Huge\$ . An inverse variation equation is $\displaystyle{y}=\frac{{k}}{{x}}\usepackage{cmbright}\Huge\$ or $\displaystyle{k}={x}{y}\usepackage{cmbright}\Huge\$ . Substitute the given values in for x and y, and then solve for k.