Downstream: The direction along with stream in water.
Upstream: The direction against with stream in water.
When the boat speed in still water is u km/hr and the stream speed is v km/hr.
Speed downstream = (u + v) km/hr.
Speed upstream = (u - v) km/hr.
When the downstream speed is x km/hr and the upstream speed is y km/hr.
Speed in still water = ½ (x + y) km/hr.
Rate of stream = ½ (x- y) km/hr.