Relative motion determines initial separation

Steps:

• Assume cars travel in the same direction; Y starts behind X by distance d.
• Relative speed of Y to X is 6 m/s - 4 m/s = 2 m/s.
• Time for Y to catch up (become level) is 20 s.
• Initial distance d = relative speed × time = 2 m/s × 20 s = 40 m.

Not enough information: The question does not define what "distance d" refers to (e.g., initial separation, total distance traveled, or something else shown in a missing diagram).

Final answer: Not enough information.