WAEC - Mathematics (1995 - No. 35)

Ae is a bisector of BAC => EAC = 45^o
CE is the bisector of ACD => ACE = 45^o
AEC = 180^o - [EAC + ACE]
 = 180^o - (45^o + 45^o) = 180^o - 90^o = 90^o