So the two opposite sides of a parallelogram is equal to each other and the two adjacent angles are supplementary. So if (x+40)+3x=180, this means that 4x+40=180. This gives us 4x=140, so x=35. If we plug it back into the equation it ascertains as such: 3(35)= 105. The answer for this question and angle O is 105 degrees, or C.
