x + y + 90 = 180 (sum of angles on a straight line)

x + y = 90 ………………….(i)

3x + 72 = 180 (sum of angles on a straight line)

3x = 108

x = 108/3 =36^O

Putting this value in eq (i), we get

x + y = 90

36 + y = 90

Y = 90 – 36 = 54^O