Identify the correct justification for each step, given that ∠1 and ∠2 are complementary, and ∠2 and ∠3 are complementary.
1. ∠1 and ∠2 are complementary
∠2 and ∠3 are complementary
2. m∠1 + m∠2 = 90°
3. m∠2 + m∠3 = 90°
4. m∠1 + m∠2 = m∠2 + m∠3
5. m∠1 = m∠3