B. 3 km
Feedback Given, speed of boat = 5 km/hr
Speed of the stream = 1 km/hr
Formula:
If the speed of a boat in still water isxkm/hr and the speed of the stream isykm/hr, then:
Speed downstream = (x+y) km/hr.
Speed upstream = (x-y) km/hr.
=>Speed downstream = 5 + 1 = 6 km/hr
=> Speed upstream = 5 - 1 = 4 km/hr
Let the required distance be 'x' km
Given , Time = 75 min = 75 / 60 hr
By formula: Time = Distance / Speed
=> (x/6) + (x/4) = 75 / 60
=> 10x / 24 = 75 / 60
=> x = (75 × 24) / (60 × 10)
=> x = 1800 / 600
=> x = 3 km