39. British navigator Captain Cook discovered a mysterious figure during his exploration. As shown in the figure, points $E, F, G$, $H$ are on the sides of quadrilateral $ABCD$, if $2AF=FB, 2CH=HD, BG=GC, DE=EA$, the area of quadrilateral $ABCD$ is 12, then the area of quadrilateral $EFGH$ is $\qquad$
$6$