Match the reasons with the statements in the proof if the last line of the proof would be 6. ∠1 and ∠7 are supplementary by definition. given: s || t prove: 1, 7 are supplementary 1. s||t given 2. ∠5 and ∠7 are supplementary. exterior sides in opposite rays. 3. m∠5 + m∠7 = 180° definition of supplementary angles. 4. m∠1 = m∠5 substitution 5. m∠1 + m∠7 = 180° if lines are ||, corresponding angles are equal.