Speed And Velocity

A motorboat whose speed is 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. What is the speed of the stream (in km/hr) ?

A speed of 50 km per hour is the same as ________ metres/ second.

Player 1 and player 2 are running around a circular field. Player 1 takes 15 minutes to take one round, while Player 2 completes the round in 25 minutes. If both start simultaneously and go in the same direction, after how much time will they meet at the starting point? (Answer to be provided only in minutes)