The answer is 100°
A parallelogram is any four sided shape with two pairs of opposite parallel and equal length sides. It is safe to say that a square is a parallelogram and not the other way round.
To explain how we got to 100 degrees, I have attached an image.
Based on the image attached, the opposite angles are equal. The adjacent angles are supplementary. With this in mind, the supplement of 80° will be 100°
