You may have thought that because 12 is 6 more than 6, LA would be 6 more than 4. However, in similar triangles, side lengths are proportional. $\displaystyle{\overline{{{L}{A}}}}\usepackage{cmbright}\Huge\$ corresponds to $\displaystyle{\overline{{{F}{I}}}}\usepackage{cmbright}\Huge\$ , and $\displaystyle{\overline{{{L}{K}}}}\usepackage{cmbright}\Huge\$ corresponds to $\displaystyle{\overline{{{F}{M}}}}\usepackage{cmbright}\Huge\$ . Now set up the correct proportion and solve.