A straight line has an angle of 180. A right angle has an angle of 90. Angle 3 is the same as angle 80°, 6, and 8. Angle 2 is the same as angle 4, 5, and 7. All you have to do is subtract the angle you know from 180, and what will be left off is Angle 3.
Then you find out what angles are the same and you have your answer.