3. As shown in the figure, the area of square $A B C D$ is $60, E$ is the midpoint of $C D$, and connect $B D$ and $A E$ intersecting at point $N$. $M$ is the midpoint of $A N$, and connect $B M$ and extend it to intersect $A D$ at point $F$. The area of the shaded part is $\qquad$ _.
$8$