Circles & Lines · Medium problem

In a rectangular box, edges $\overline{AB}$, $\overline{AD}$, and $\overline{AE}$ meet at corner $A$ and are mutually perpendicular, with $AB = 3$, $AD = 6$, and $AE = 9$. What is the distance from $A$ to the plane through $B$, $D$, and $E$?