Question on: WAEC Mathematics - 1995

a + c + d - 180^o[sum of angles in triangle]
x = a[vertical opp. ∠s]
y + x + d = 180^o[sum of ∠s in a Δ]
y + a + d = 180^o
y + a + d = a + c + d
y = c
but b + y = 180^o [sum of ∠s on a straight line ]
b + c = 180^o; Ans = A = 180^o