A train 75 m long overtook a person who was walking at the rate of 6 km/hr and passes him in 7 1/2 seconds. Subsequently it overtook a second person and passed him in 6 3/4 seconds. At what rate was the second person travelling?

A. 4 km/hr
B. 2 km/hr
C. 1 km/hr
D. 5 km/hr