Answer: The sum of 3 angles in a triangle always is 180º, the answer is B
Explanation:
You see, the small triangle?
The sum of 3 angles is 180º, and we know 2 angles is 70º and 30º, so the left angle is equal to 180º-70º-30º=80º
Now, you look at the biggest triangle we have.
We have the top angle, is 80º that we found before, so a+b=180º-80º=100º