Answer:
b) 4.5 hours
Explanation:
The first cyclist has a 3-hour head start. At 6 mph, that is an 18-mile head start.
The second cyclist gains on the first at the rate of (10 -6) = 4 mph, so will make up that 18 miles in ...
(18 mi)/(4 mi/h) = 4.5 h
The second cyclist will catch up with the first after 4.5 hours from the time the second cyclist started.