Question 331380
Two cyclists start biking from a trail's start 3 hours apart. The second cyclist travels at 10 miles per hour and starts 3 hours after the first cyclist who is traveling at 6 miles per hour. How much time will pass before the second cyclist catches up with the first from the time the second cyclist started biking? 
---------------------
In 3 hours, the 1st cyclist is 18 miles ahead (3*6).
The 2nd cyclist gains on him at 4 mph (10 - 6).
18/4 = 2.25 hours
---------------------
There are other ways to do it, more math, more equations, more work.
I don't recommend them.