Quantitative aptitude

Two friends A and B run around a circular track of length 510 meters, starting from the same point, simultaneously and same direction. A who runs faster than B in the middle of 5th round. If A and B were to run a 3 km race long, how much start in terms of distance, should A give B so that they finish the race in dead heat?

a)545.45m

b)666.67m

c)857.14m

d)cannot be determined

need full detailed explanation