∴∠CEB+∠B=90 ,∴∠BCE=90，

∫ab = 10, AE=DC=5, ∴BE=5, CE=AD=4, at RT△BCE, BC=3,

∴S△BCE=6, if c is CF⊥AB in f, S△BCE= 1/2*BE*CF, ∴CF= 12/5.

Trapezoidal area s =1/2 (CD+ab) * cf =1/2 (5+10) *12/5 =18.