12. using the diagram, what can be said about angles 7 and 12?
a. they're congruent.
b. we can't determine from the given information.
c. they're supplementary.
d. they're complementary.

They are supplementary because angle 12 is congruent with angle 10 which is supplementary with angle 7 ( that means the measure of angle7+ the measure of angle 12 is 180 grades)
12 and 10 are congruent due to the fact that A and B are two parallel lines and D is a sequent (i don't know how to spell this word). i guess you get it

Set up a system of equations