We have,
x+80o+100o+40o=360o(Verticaloppsiteangle)
x=360o−220o
x=140o
Now,
x+y=180o(LinearPair)
⇒140o+y=180o
⇒y=180o−140o
⇒y=40o
Hence, this is the answer.
If the angle of incidence is 30∘ then find the unknown angle.