Because f and j are the midpoint of CD and BC respectively, then FJ is parallel to BD, and its length is equal to half of BD.

Similarly, EJ is parallel to AC and EJ is equal to half of AC.

So FJ=EJ, EFJ angle is equal to FEJ angle.

Because FJ is parallel to BD, OGH angle is equal to e FJ angle.

EJ is parallel to AC, and the angle OHG is equal to FEJ.

So the angle OGH equals the angle OHG.

So OG = oh