Given: ∠1 and ∠2 are supplementary; ∠1 and ∠3 are supplementary
Prove: ∠2 ≅ ∠3

Statements
1. ∠1 and ∠2 are supplementary
2. m∠1 + m∠2 = 180°
3. ∠1 and ∠3 are supplementary
4. m∠1 + m∠3 = 180°
5. m∠1 + m∠2 = m∠1 + m∠3
6. m∠2 = m∠3
7. ∠2 ≅ ∠3

I need the reasons for these statements.