Answer:
See explanation
Explanation:
16. Two parallel lines are cut by transversal. Angles with measures
and
are alternate exterior angles. By alternate exterior angles, the measures of alternate exterior angles are the same:

Then

17. Two parallel lines are cut by transversal. Angles with measures
and
are alternate interior angles. By alternate interior angles, the measures of alternate interior angles are the same:

Then

18. Two parallel lines are cut by transversal. Angles with measures
and
are alternate exterior angles. By alternate interior angles, the measures of alternate exterior angles are the same:

Then

19. The diagram shows two complementary angles with measures
and
. The measures of complementary angles add up to
then

Hence,

Check:

20. Angles
and
are vertical angles. By vertical angles theorem, vertical angles are congruent, so

Hence,

21.
and
are supplementary. The measures of supplementary angles add up to
so

Therefore,
