solution for question 3

Let the speed of the stream be x km/hr. Then,

Speed downstream = (15 + x) km/hr,

Speed upstream = (15 - x) km/hr.

	30	+	30	= 4	1
	(15 + x)		(15 - x)		2

	900	=	9
	225 - x2		2

 9x² = 225

 x² = 25

 x = 5 km/hr.