Final answer:
To solve for x, use the fact that line segment AB bisects line segment CD and set up an equation with the given lengths of CD and CB. Solve the equation to find x.
Step-by-step explanation:
To solve for x, we can use the fact that line segment AB bisects line segment CD. This means that the length of segment CB is equal to the length of segment CD. Given that CD = 42 and CB = 3x + 9, we can set up an equation: 3x + 9 = 42. Next, we can solve for x by subtracting 9 from both sides of the equation and then dividing by 3. This gives us the solution x = 11. Therefore, none of the given options A, B, C, or D is correct.