Problem: An 18-year-old runner can complete a 10.0-km course with an average speed of 4.38 m/s. A 50-year-old runner can cover the same distance with an average speed of 4.15 m/s.
Part A: How much later (in seconds) should the younger runner start in order to finish the course at the same time as the older runner?
I want to know how to work this out step by step, not just the answer please.