12. As shown in the figure, $A D$ is the angle bisector of $\triangle A B C$, and the perpendicular bisector of $A D$ intersects the extension of $B C$ at $F$. If $\frac{A C}{A B} = \frac{3}{4}$, then $\frac{C F}{B F}=$ $\qquad$
12. $\frac{9}{16}$