Answer:
27. Alternate exterior angles are congruent.
28. Same-side interior angles are supplementary.
Explanation:
27. The two angles whose measures are set equal by the equation are on opposite sides of the transversal, so are "opposite." They are "outside" the space between the parallel lines, so are "exterior." These descriptors identify the angles as "opposite exterior" angles. The theorem/postulate that lets you set their measures equal is ... [the one written above].
28. The two angles whose measures are added in the equation are on the same side of the transversal, so are "same-side" angles. They are "inside" the space between the parallel lines, so are "interior." These descriptors identify the angles as "same-side interior" angles. The theorem/postulate that says their measures sum to 180° is ... [the one written above].