Without telling Sally, Joe made travel arrangements that include a stopover in Toronto to visit Joe’s old buddy. Sally doesn’t like Joe’s buddy and wants to change their tickets. She hops on a courtesy motor scooter and begins accelerating at 0.9 m/s² toward the ticket counter to make arrangements. As she begins moving, Joe is 40 m behind her, running at constant speed of 9 m/s.

(a) How long does it take for Joe to catch up with her? 

(b) What is the time interval during which Joe remains ahead of Sally?