Answer:
40 degrees
Explanation:
We know that the base angles are congruent (a fancy word for equal) because of the slash marks. This means that both of the base angles are 70.
Every triangle adds up to 180 degrees.
So, You can just do 180 - (70+70)
Algebra version:
70 + 70 + x = 180
140 + x = 180 (subtract 140 on both sides)
x = 40
hope this helps :)