Verified answer

suplemento = 180-x

complemento = 90-x

(180-x) = 3.(90-x) + 50

180-x = 270-3x + 50

2x = 140

x = 70º

.........

(180-x) + 50 = 3(90-x)

180 - x + 50 = 270 - 3x

2x = 40

x = 40/2

x = 20

medida do angulo 20º