Consider the triangle (in which angle4 is present)
by angle sum property,
20 + 40 + angle4 = 180
60 + angle4 = 180
angle4 = 180 - 60
angle4 = 120
Also,
angle2 = 120 (vertically opposite angles)
angle1 + angle2 = 180 (linear pair)
angle1 + 120 = 180
angle1 = 180 - 120
angle1 = 60
