So we know that a triangle equals 180 degrees. You can subtract 20 from 35 and get 15. !5 would be the missing value for the first triangle. Also since you have a vertical angle, missing angle would be 15 as well. Now you can do 180-156 because it is linear. You would get 24. And now for this step, I think you subtract 24-15 to get the missing value which is 9.
