Answer:
an exercise left to the student
Explanation:
This requires careful construction with a compass and straightedge on the original worksheet. You need to find the point of intersection of the perpendicular bisectors of EE', FF', and GG'.
My estimate is that the point of intersection is in the neighborhood of (4.5, 3), but I cannot be sure with the distorted image.
Point D may be near (4.5, 3).