B is the midpoint of AC . find the following #6 and #7 please

Answer: x = 25
ab = 42
BC= 42
ac = 84
I need #6
Step-by-step explanation:
6. Find what x is by setting each value equal to each other
2x - 8 = x + 17
x - 8 = 17
x = 25
ab = 42
BC= 42
ac = 84