10. The area of square $A B C D$ is 9 square millimeters, and the area of square $E F G H$ is 64 square millimeters. As shown in the figure, side $B C$ lies on $E H$. It is known that the area of triangle $A C G$ is 6.75 square millimeters, then the area of triangle $A B E$ is $\qquad$ square centimeters.
$2.25$