A man rows a distance of 16 km upstream in 4 hours, while he rows a distance of 36 km downstream in 6 hours. What is the speed of the stream?

A bus travels 57 part of its total journey at its usual speed. The remaining distance is covered by the bus at 14 of its usual speed. Due to reduced speed, it reaches its destination 180 minutes late. If the total distance is 280 km, what is the usual speed of the bus?

A train traveling at a speed of 45 km/h crosses a pole in 24 seconds. What is the length of the train?