Question 309693
18 year old runner distance 10 km - speed = 4.63 m/sec.
50 year old runner distance 10 km  -3.82 m /sec

The distance is in km and speed in m/sec.

convert distance to meters

10km = 10,000 meters.

time taken by 18 year old = 10000/4.63
= 2159.82 seconds
.
time taken by 50 year old = 10000/3.82
= 2617.80 seconds
457.98 seconds

He can start 458 seconds later to reach at the same time