Use the equation for joint variation and the given values for x, y, and z to find k.

$\displaystyle{y}={k}{x}{z}\usepackage{cmbright}\Huge\$

$\displaystyle{360}={k}{\left({4}\right)}{\left({10}\right)}\usepackage{cmbright}\Huge\$

$\displaystyle{360}={40}{k}\usepackage{cmbright}\Huge\$ , so $\displaystyle{k}={9}\usepackage{cmbright}\Huge\$

Use this value of k and the given second set of values for x and z to find y:

$\displaystyle{y}={9}{\left({5}\right)}{\left({12}\right)}\usepackage{cmbright}\Huge\$ or $\displaystyle{y}={540}\usepackage{cmbright}\Huge\$