Given that:

And given that these angles are Complementary (they add up to 90 degrees):

22. A Right Angle is an angle that measures 90 degrees. Therefore, by the definition of Right Angles:

23. According to the Angle Addition Postulate, if two or more angles are next to each other and have a common vertex, then the total measure of the angle is obtained by adding them.
Therefore, in this case:

24. The Substitution Property of Equality states that, if:

And:

Then:

Applying that property, you can set up that:

25. By definition, Complementary Angles add up to 90 degrees.
Knowing that angles EFG and ABC are Complementary, you know that:

26. The Transitive Property of Equality states that if:

And:

Then:

Therefore:

27. According to the Congruent Complements Theorem, two angles have the same measure of they are complementary to the same angles. In this case:

28. By definition, if two angles are congruent, they have the same measure.
Hence, the answer is.
22. Definition of Right Angles.
23.

24. Substitution Property of Equality.
25. Definition of Complementary Angles.
26 Transitive Property of Equality.
27. Congruent Complements Theorem.
28. Congruence Definition.