I don’t quite understand the solution to this following problem:

Cecil and Levi are running clockwise on 1000 meter track circular track at constant speeds of x and 6 meters per second respectively. Cecil is 400 meters behind Levi.

Quantity A: The time it would take for the two to be at the same point on the tack if x=7

Quantity B: The time it would take for the two to be at the same point on the track if x=4.5