In the diagram PQR is a straight line m n 120o ... - WAEC Mathematics 2014 Question

if m + n = 120^o and n + r = 100^o

then m + n = 120^o

then r = 180^o - 120^o = 60^o

also n + r = 100^o

m = 180^o = 80^o

m + r is = 80^o + 60^o

= 140^o