Aboat travels upstream from B to A and downstream from Ato B in 3 hours. If the speed of the boat in still water is 9 km/hour and the speed of the current is 3 kn/hour, what is the distance between A and B?
Let the distance between A and B = 'D' km
Sspeed of the boat in still water =9 km/h
Sspeed of the current =3 km/h
Upstream speed = 9 - 3 = 6 km/h
Downstream speed = 9 + 3 = 12 km/h
Now,
$$\frac{D}{6} + \frac{D}{12} = 3$$
2D + D = 36
D = 12 km