Correct Answer - Option 1 : 16 km / h
Given:
Speed of stream = 6 km / h
Distance upstream = 14 km
Time = 84 min
Formula used:
Downstream speed = Speed of Boat + Speed of stream
Upstream speed = Speed of Boat - Speed of stream
Calculations:
Rate Upstream = 14 / 84 × 60 = 10 km / h
Speed of Stream = 6 km / h
Let speed in still water be x.
Then, Upstream speed = (x - 6) km / h
∴ x - 6 = 10
⇒ x = 16 km / h
The speed of the boat in still water is 16 km / h.