We choose a point on each side of a parallelogram $ABCD$, let these four points be $P, Q, R$ and $S$. Then we divide the parallelogram into several regions using line segments as shown in the figure. The areas of the grey regions are given, except for one (see the figure). Find the area of the region marked with a question mark.
Problem
Source: 2019 Dürer Math Competition Finals Day2 E7 E+6 https://artofproblemsolving.com/community/c1621835_2019_
Tags: geometry, areas, parallelogram
