Question

a streamer goes downstream and covers the distance between two ports in 4 hours while it cover the same distance upstream in 5 hours if the speed of the stream bee 2 km per hour find the speed of the steamer in still water

Answer 1

Let the distance between the two ports be x km. 
Then, speed downstream = x/4 
And speed upstream = x/5 
Speed of the stream, 
= [speed downstream - speed upstream] / 2
= (x/4 - x/5)/2
Or, (5x -4x)/40 = 2
Or, x/40 = 2 
Thus, x = 80 km.
Distance between two ports = 80 km.

Answer 2

Let the steamer speed will be x.

Downstream speed = (x+2)

Distance between the points = 4(x+2)    ---------- (1)

Upstream speed = (x-2)

Distance between the points = 5(x-2)     ------------ (2)

On solving (1) and (2), we get

4(x+2) = 5(x - 2)

4x + 8 = 5x - 10

x  = 18

speed of the steamer in still water = 18 km/hr