Becky completed the proof incorrectly.

Step-by-step explanation:

The only difference of the two proofs, at least what I can see, is the reason for step 2. Angie claims that it is the Definition of Supplementary Angles, while Becky claims Angle Addition Postulate.

The Definition of Supplementary Angles states that m∠A + m∠B = 180°.

While the Angle Addition Postulate states that m∠A + m∠B = m∠C.

Because the context used is that m∠AKG + m∠GKB = 180° and m∠GKB + m∠HKB = 180°, it would be using the Definition of Supplementary Angles.

So Becky is the one who is incorrect.