The line a and line b are parallel to each other since if you draw another line or a third plane and it contains both points both in line a and in line b it means that this third plane passes through to the both lines a and b. In order to achieve both lines a and b can be passed by the third plane, they should be parallel to each other.
B would be 11 (if thats what youre asking)
Hope this helps!
Answer:
19
Step-by-step explanation:
15z-14z=12+7
z=19
