Answer:
20°
Step-by-step explanation:
take the sum of 3y + 10 and y and equal it to 90° that creates an equation making it easier for you to continue
let's assume the opposite angle of Y to be X
angle Y = angle X ( vertically opposite angles)
3y + 10 + X + 90° = 180° ( forming linear pair)
3y + X + 100 = 180°
X + 3y = 80° ----(1)
Y + 3y = 80°
4y = 80°
y = 20°
