IBPS RRB PO Mains 25 Sep 2021 Paper

A boat has speed a of 15 m/s in still water, but while going upstream its speed is half the speed as compared to the speed of the boat going downstream. The boat is going downstream and a ship while going downstream crosses the boat in 15 seconds. The length of the ship is double the length of the boat. Find the time the ship will take to cover a distance of 144 kilometers while going upstream if the length of the ship is 100 meters.