The speed of a boat is 10 km/h in still water. It covers a distance of 90 km in 15 hours going upstream. What is the speed of the stream?A6 km/hB3 km/hC5 km/hD4 km/hAnswer: D. 4 km/h Read Explanation: Let speed of the stream be x km/h Upstream speed = 90/15 = 6 km/h 6 = (10 - x) ⇒ 6 = (10 - x) ⇒ x = 4 km/hRead more in App