5. As shown in the figure, in $\triangle A B C$, $\angle A=90^{\circ}, \angle A B C=30^{\circ}, D$ is the midpoint of $A C$, $C E$ is the angle bisector of $\angle A C B$, and $B D$ intersects $C E$ at point $F$. The area of $\triangle A B C$ is 100, then the area of $\triangle B C F$ is . $\qquad$
$40$