In river A, the distance travelled by a boat downstream in time T is 50% more than the distance travelled by the same boat upstream in the same time. In river B, the same boat travels a distance of 11 km upstream in 30 minutes. If the speed of the current in river B is 2 km/h, what is the speed of the stream in river A? (The speed of the boat in still water is same in both the rivers)