In a parallelogram the 4 angles need to sum to 360 degrees. There are two sets of identical angles, so one of the other angles would also be 80 degrees.
Now find the other two angles:
360 - 80 - 80 = 200 degrees
200 degrees / 21 = 100 degrees each.
The other 3 angles are: 80, 100 and 100
