The distance between two points on a river is D km. A man rowing a boat along the stream finds that the distance of rowing along the stream is 30 times the total distance and when he started rowing against the stream the distance he rowed was found 4 times of total distance. The total time taken along the stream is 10% more than that against the stream. If the boat cover 135 km along the stream in 9 hours. What is the speed of stream?