Answer: 140 degrees
Explanation:
Angle 4 = angle 1 (vertical angles)
angle 1 = angle 2 (alternate interior angles)
angle 4 = angle 2 (transitive property)
angle 4 = 40
angle 2 = 40
angle2+angle3 = 180 (linear pair)
angle3 = 180-angle2 = 180-40 = 140
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A quicker method is to use the same side exterior angle theorem which says that the same side exterior angles are supplementary (meaning the angles add to 180 degrees). So angle4+angle3 = 180 leads to angle3 = 140.
