It's a rectangle with uniform density.
I would situate it on a set of coordinate axes, with A at the Origin and B on the Positive x-axis. This puts D on the Positive y-axis.
Area of FDE = ??
Area of AFECB = ??
Center of Mass of FDE = (??,??)
Center of Mass of AFECB = (??,??)
Fill in the blanks and let's see where that leads us?