Let the speed of boat in still water be x km/hr and the distance be y km. Rate downstream = (x + 3) km/hr Rate upstream = (x – 3) km/hr According to the question, y/(x + 3) = 1 --- (i) y/(x – 3) = 3/2 --- (ii) On dividing equation (i) by (ii), (x – 3)/(x + 3) = 1/(3/2) = 2/3 3x – 9 = 2x + 6 x = 9 + 6 = 15 kmph