The answer is A because in a triangle, the angles need to add up to 180 degrees. In the triangle, the missing angle would be 65 because 180 - (75 + 40) = 65. Now you know the missing angle in the triangle is 65. But you’re trying to find the other angle that would make this pair supplementary (180 degrees). You would do 180 - 65 to get your answer to the problem of 115 or A.