Since all triangle's angle's values add up 180 degrees, this means we have to make sure to angles add up to 180.
A. 75 + 35 = 110. 180 - 110 = 70 degrees.
B. This triangle is isosceles meaning 2 of its sides is the same length. In this case, the two sides add up to 140 (meaning they are both 70 degrees). 180 - 140 = 40 degrees.
C. I sadly don't know how to solve it.
D. This is another isosceles triangle. 180 - 36 = 144.