You may have substituted correctly into a joint variation equation, but then reversed the numbers when dividing and solving. Using the equation $\displaystyle{32}={k}{\left({20}\right)}{\left({2}\right)}\usepackage{cmbright}\Huge\$ , multiply to find $\displaystyle{32}={k}{\left({40}\right)}\usepackage{cmbright}\Huge\$ . Divide to solve for k.