The angle at the top left of the parallelogram = 120°
Let the other unknown part of this angle = y
So.....we have this system
3x + y = 120 → y = 120 - 3x (1)
2x + 90 + y = 180 → 2x + y = 90 → y = 90 - 2x (2)
Set (1) = (2)
120 - 3x = 90 - 2x
120 - 90 = 3x -2x
30° = x
