The Rajdhani train travels in a straight line at a constant speed of 75 km/h for a particular distance ‘d’ and then travels another distance equal to ‘2d’ at a constant speed of 100 km/h in the same direction as earlier. Find the average speed of the train during the whole journey?

A

84 km/h

B

90 km/h

C

96 km/h

D

88 km/h