Answer:
1) a. Verticle angles are congruent
3) b. Same-side interior angles are supplementary
5) d. Alternate interior angles are congruent when the lines are parallel
6) c. Substitution
Explanation:
1) ∠1 and ∠2 are vertical angles, they're congruent
3) ∠2 and ∠3 are same-side interior angles which are supplementary (add up to 180)
5) ∠3 and ∠4 are alternate interior angles meaning they're congruent
6) idrk how to explain it but its the last one so substitution goes with it :)