Question

After how much time would they meet for the first time at a point diametrically opposite to the starting point on the track?

Answer 1

When two persons A, and B are running around a circular track of length L mts with speeds of a, b m/s in the same direction
They meet each other at any point on the track is L(a−b) seconds

They meet each other at exactly at the starting point =  (La,Lb) seconds