Thanks @jamiezue & @dilann for the solutions. @jamiezue , you made an error in the area of the triangle BCD. But very close to the actual.
The simplest approach (possibly)... We immediately know the sides of the triangle BCD.
BC = 13, BD = SQRT (18^2 + 6^2) = 6√10, CD = SQRT(6^2+5^2) = √61
Now...