A boat which has a speed of 5Kmph in still water crosses a river of width 1 Km along the shortest path in 15 minutes. Velocity of river in kmph is

V¯BR=5 kmph                 W = 1 km                tshortestpath=15min=14hr                VR=?                t=152−VR2=14                125−VR2=116                25−16=VR2                ⇒VR=3 kmph