Rahul and Rohan were assigned two different delivery locations such that the distance of their locations from their warehouse (both start from the same warehouse) is 40 km and 50 km respectively. Both of them leave the warehouse at the same time and reach their respective locations at 10
A.M. One day, the locations assigned to them are interchanged, and Rahul started 15 minutes earlier than Rohan to reach his new location at the scheduled time. Find the speed of Rahul.

Distance covered by Rahul and Rohan = 40 km and 50 km, respectively.
Since, both of them reached their respective places at same time.
Therefore, ratio of speeds of Rahul and Rohan = 40:50 = 4:5.
Let the speeds of Rahul and Rohan be 4x km/hr and 5x km/hr, respectively.
Time taken by Rahul to reach his place on the day of interchange = 50/4x hours.
Time taken by Rohan to reach his place on the day of interchange = 40/5x hours.
ATQ, (50/4x) – (40/5x) = 15/60.
Or, 12.5/x - 8/x = 0.25.
Or, 4.5/x = 0.25.
Or, x = 18.
So, speed of Rahul = 4x = 72 km/hr.
Hence, the correct answer is B.