Answer:

Step-by-step explanation:
Part 1) If line a is parallel to line b
then
-----> by alternate exterior angles
so
we have

therefore

Part 2) we know that
-----> by supplementary angles
we have

substitute
Part 3) If line a is parallel to line b
then
-----> by alternate interior angles
so
we have
therefore
Part 4) If line b is parallel to line c
then
-----> by corresponding angles
so
we have
therefore