Ritu can row downstream 20 km in 2 hours and upstream 4 km in 2 hours. Find her speed of rowing in still water and the speed of the current.

let the speed of ritu in still water be x km /hr and current be y km /hr 

then , for downward , speed = x+y            then ,  t = d/s            => t = 20/ x+y               => 20/ x+y =2 

or , x+y = 10 ..............(1)

 and for upstream = x-y                        then ,  t = d/s                => t = 4/ x-y        => x-y =2 .....................(2)

then from 1 and 2          we get

x+y +x-y = 10+2         => 2x =12     => x =6 

then y = 10-6 =4 

then speed in still water = 6 km/hr   adn current = 4 km/hr