You may have found the correct value of k, but then chose the two measurements whose sum is 60. However, the numbers need to satisfy $\displaystyle{y}=\frac{{k}}{{x}}\usepackage{cmbright}\Huge\$ , an inverse variation equation. For the first triangle, $\displaystyle{10}=\frac{{k}}{{6}}\usepackage{cmbright}\Huge\$ , so $\displaystyle{k}={60}\usepackage{cmbright}\Huge\$ . Substitute 40 and 20.

$\displaystyle{40}=\frac{{k}}{{20}}\usepackage{cmbright}\Huge\$ does not yield $\displaystyle{k}={60}\usepackage{cmbright}\Huge\$ , so this is not an inverse relationship.