Question on: WAEC Mathematics - 2014

y + z = 180^o

z = 180^o - y

x + k = 180^o

k = 180^o - x

the sum of angles in the (\bigtriangleup) are: n + z + k = 180

but n + 180^o - y + 180^o - x = 180^o

n + 180^o - y - x = 0

but we want to find n

n + 180^o = x + y

but x + y = 220^o

n + 180^o = 220^o

n = 220^o - 180^o

n = 40^o