∴ Quadrilateral AEBD is a parallelogram,

∴S△ABE=S△ABD.

In the diamond ABCD,

S△ABD=S△BCD= 12S rhombic ABCD =12×12× 6× 8 =12.

∴ The area of quadrilateral AECD is equal to 12× 3 = 36.

So choose a.