Correct. Set up a proportion using corresponding sides: $\displaystyle\frac{{{A}{B}}}{{{D}{E}}}=\frac{{{A}{C}}}{{{D}{F}}}\usepackage{cmbright}\Huge\$ . Substitute the given side lengths into the equation, and let n stand for AB: $\displaystyle\frac{{n}}{{6}}=\frac{{12}}{{8}}\usepackage{cmbright}\Huge\$

Multiply both sides by 6 to solve: $\displaystyle{n}=\frac{{72}}{{8}}={9}\usepackage{cmbright}\Huge\$