WAEC - Mathematics (1995 - No. 40)

ACB = ABC [Base angles of isoceles triangle]
ACB + ABC + 50^o = 180^o[sum of angles in a triangle]
ACB + ABC = 180^o - 50^o = 130^o

ACD + ACB = 180^o[sum of ∠s on a straight line]
ACD + 65^o = 180^o
ACD = 180^o - 65^o = 115^o