You may just have multiplied 35 by 20. Be sure to use the joint variation equation $\displaystyle{y}={k}{x}{z}\usepackage{cmbright}\Huge\$ to find the constant of variation, k. Then use that value of k, along with the second set of values for x and z, in a second joint variation equation to solve for y. The correct answer is 350 square centimeters.