A boat takes 3 hours to travel from point B to point A against the current and then return from A to B with the current. Given that the boat's speed in still water is 9 km/h and the current flows at 3 km/h, what is the distance between points A and B?

Explanation

The boat's effective speed downstream is 9 km/h + 3 km/h = 12 km/h, while upstream speed is 9 km/h - 3 km/h = 6 km/h. Let the distance between A and B be x km. The total time taken is the sum of upstream and downstream times: x/6 + x/12 = 3 hours. Multiplying both sides by 12 gives 2x + x = 36, so 3x = 36, resulting in x = 12 km.