The correct response for the blank in statement 2 ("m∡A = m∡E") is:
Transitive Property of Equality
Here's the reasoning:
In the proof, you have m∡A = m∡C (from statement 1, combined with the fact that angles A and C are supplementary). Because m∡A = m∡E (statement 2) and m∡E + m∡C = 180° (statement 3), you can use the Transitive Property of Equality to show that if m∡A equals both m∡E and m∡C, then m∡E must also equal m∡C.
So, the completed statement 2 would read:
2. m∡C = m∡E (by Transitive Property of Equality)