If the inside angles of the parallelogram are 60 and 120, then you may add the two 60 degrees adjacent angles together.
Adjacent angles in a polygon are those that share a side. If the angles in a parallelogram are 60-120-60-120, then the angles 60 & 60 are opposite angles, as also the pair 120 & 120.
If you take any two adjacent angles, one of them will be 60 and the other one is 120.
Here is the picture of two adjacent angles in a parallelogram: