In water, the direction along the stream is called Downstream. And the direction against the stream is called Upstream.
If the speed of the boat in still water is u km/hr and the speed of the stream is v km/hr, then:
Speed downstream = (u + v) km/hr
Speed upstream= (u - v) km/hr
If the speed downstream is a km/hr and the speed upstream is b km/hr, then:
Speed in still water = 1/2 (a + b) km/hr
Rate of the stream = 1/2 (a - b) km/hr
When the distance covered downstream and upstream are equal, we can write: (u + v)t1 = (u - s)t2 where t1 and t2 are different time taken.