To find the measure of the third, we need to know that the sum of the inside angles of a triangle is 180°:
So 102.9 + 40.4 + x = 180
Where x is the third angle.
Then solve the equation for x to know the value:
102.9 + 40.4 + x = 180
40.4 + x = 180 - 102.9
x = 180 - 102.9 -40.4
x = 36.7
The measure of the third angle is 36.7°
The correct answer is option D.