Change 40 m/sec into km/hour

Conversion of m/sec to km/hr

Two trains, one is of 121 m in length at the speed of 40 km/hour and the other is of 99 m in length at the speed of 32 km/hour are running in opposite directions. In how much time will they be completely clear from each other from the moment they meet ?

Change the speed of 6 m/s into km/h.

A boat goes 40 km upstream in 8 hours and 36 km downstream in 6 hours. The speed of the boat in still water is