Correct option is (A) 80°
\(\because\) Sum of adjacent angles in a parallelogram is \(180^\circ.\)
Since, \(\angle S\;\&\;\angle O\) are adjacent angles in parallelogram SOAP.
\(\therefore\) \(\angle S+\angle O\) = \(180^\circ\)
\(\Rightarrow\) \(\angle O=180^\circ-\angle O\) \(=180^\circ-100^\circ=80^\circ\) \((\because\angle S=100^\circ)\)
