Answer:
x = 0
x = 3
Step-by-step explanation:

True. The midsegment of a triangle is halfway up the triangle, and since the top half and the full triangle are similar triangles, its dimensions are proportional.
This means half the height will give half the base (midsegment). So the midsegment is always half the length of the side it's parallel to.
Coefficient is the correct answer
2z+6+15-9z
-7z+21
Hope this helps