Question 500240
Let b be the speed of the boat in still watetr and c be the rate of the current.

Using the formula, distance = speed * time

In dowmstream
    26 = (speed of boat + speed of current) * t
    26 = (b + c) * 2
=> b+c = 13   -> equation 1

In upstream,
     26 = (speed of boat - spead of current) * t
     26 = (b - c ) * 4

=> b -c = 6.5  -> equation 2

eqution 1 - equation 2
   2b = 19.5
=> b = 9.75 km/hr 
speaad of boat in still water = 9.75km/hr
   c = 13 - b ( from eqiation 1)
   c= 13 - 9.75
      = 3.25 km/hr

=> Speed of current = 3.25km/hr

Check:
   b+c = 13  (equation 1)
   9.75 + 3.25 = 13
    b-c = 6.5  (equation 2)
    9.75 - 3.25 = 6.5