All of the angles in a triangle add up to 180 so you can set this equation up:
2x - 10 + x + 30 + 70 = 180
Now combine lie terms.
3x + 90 = 180
Subtract 90 from both sides.
3x = 90
Now divide three from both sides to get x.
x = 30
Now you know x so plug it into angle A to get the answer
2 (30) - 10
60 - 10
50
50 is the value of angle A!
Hope that helps! Let me know if you have any questions!
- mathwizzard3
