Answer:
see answer below.
Step-by-step explanation:
So m∠1= 40, as given in the question.
We should already know that a straight line, or angle, is equal to 180°
Knowing that it is equal to 180°, to find the angle of ∠3, you can subtract 40 from the 180°
180°-40°= 140°
answer: m∠3= 140°
