Incorrect. Substitute into the joint variation equation $\displaystyle{y}={k}{x}{z}\usepackage{cmbright}\Huge\$ to get: $\displaystyle{320}={k}{\left({4}\right)}{\left({16}\right)}\usepackage{cmbright}\Huge\$

Solve for k. Then use that value for k and the second given values for x and z in a new joint variation equation to solve for y. The correct answer is 400.