Answer: 15
Step-by-step explanation:
By the trapezoid midsegment theorem,

It would be the last option. I just worked the problem out and figured it out. I hope this helped! (:
1)81° due to the fact that 99° and (1) are supplementary angles
2)99° due to the fact that (5) and (2) are adjacent angles that sum up to equal 180°
3)81° due to the fact that it is the corresponding angle to (5)
4)99° due to the fact that (4) and (2) are alternate interior angles which equal the same
5)81° due to the fact that (5) and (6) are adjacent angles which means they are supplementary angles that add to equal 180°
6)99° due to the fact that (6) and (2) are corresponding angles which equal the same value
7)81° due to the fact that (7) and (3) are corresponding angles with equal the same degree
I have no idea.... Try to ask your teacher or your parents