The line in the middle is half the length of the line on the outside. Multiply the middle line by 2 and set it equal to the outside line.
2(x-3) = x + 6
Simplify:
2x -6 p x + 6
Add 6 to both sides
2x = x + 12
Subtract x from both sides:
X = 12
The answer is B) 12