Question 111108
Sure, I will help you.

Let x mil/hr be the speed of the boat and y mil / hr be that of the current.

Down stream they travelled 55 miles in 5 hrs

==> their speed = distance/time

                 = 55/5

                 = 11 miles/hr

Actually downstream the speed = speed of boat + speed of current

==> x + y = 11 ---------------(1)

Up stream they travelled 55 miles in 11 hrs
==> their speed = distance/time
                = 55/11
                = 5 miles/hr

upstream the speed = speed of boat - speed of current
==> x - y = 5  ---------------(2)

(1) - (2) gives 2y = 6

==>  y = 6/2
       = 3

Thus the speed of the current = 3 miles/hr


Good luck!!!