The downstream speed of boat A is 21 km/hr 21 \text{ km/hr} 21 km/hr . The speed of boat B in still water is 12 km/hr 12 \text{ km/hr} 12 km/hr , and ...
Question
The downstream speed of boat A is . The speed of boat B in still water is , and the ratio of the speed of boat A to boat B in still water is , respectively. Given that the speed of the stream is the same for both boats, find the time taken by boat B to cover upstream.