∠2-∠ 1=40

So ∠ 1 = 20, ∠ 2 = 60.

In the sense, we know that ∠2 is ∠ 1.

adjacent angle

, ∠3 is the adjacent angle of ∠2, ∠4 is the adjacent angle of ∠3 and ∠ 1

Drawing, we know that there is only one case where ∠4 is the adjacent angle of ∠3 and ∠ 1 and ∠ 1+∠2 is not equal to 180.

That is ∠ 1+∠ 2+∠ 3 = 180, ∠ 4 = 180.

So ∠ 3 = 180-20-60 = 100.

So ∠3 = 100∠4 = 180.

Hope to adopt, thank you!