Let upstream speed = S_{u} kmph

and downstream speed = S_{d} kmph.

Then, ...(1)

and ...(2)

Adding (1) and (2), we get :

...(3)

Subtracting (1) and (2), we get :

....(4)

Adding (3) and (4), we get : or S_{u} = 8.

So,

⇒ S_{d} = 12.

∴ Speed upstream = 8 kmph,

Speed downstream = 12 kmph.

Hence, rate of current

= kmph = 2 kmph.