Let the speed of motor boat in the still water = x Speed downstream = x + 6 Speed upstream = x - 6 Distance covered in both ways is equal so, (x + 6) 6 = (x - 6) 8 6x + 36 = 8x - 48 2x = 84 x = 42 km/hour So, speed of the motor boat in the still water = 42 km/hour