A motor boat whose speed is 9 km/hr in still water, goes 15 km downstream and comes back in a total

Описание: A motor boat whose speed is 9 km/hr in still water, goes 15 km downstream and comes back in a total time of 3 hours 45 minutes. Find the speed of the stream.
class 10 maths RS Agarwal, chapter name- Quadratic Equations, chapter number 10, exercise number - 10E, question number - 53.
class 10 maths RS Agarwal.