Given, AOB is a straight line In the given figure, ∠AOC+∠COD+∠DOE+∠EOB=180∘ [Angles on a straight line] ⟹35∘+45∘+4a∘+40∘=180∘
⟹4a+120∘=180∘
⟹4a=180∘−120∘
⟹4a=60∘ ⟹a=15∘