We know that O is midpoint of BF, which means OF is equal to OB by definition of midpoint.
Also, angles FOE and BOA are congruent by vertical angles theorem. Angles B and F are congruent by given, both are right angles.
We can deduct that triangles EFO and ABO are congruent by ASA postulate of congruence.
From the congruence between triangles, we deduct that angles A and E are congruent.
