the speed at which a man can row a boat in still water is 15 km / hr . if he rows downstream , where the speed of current is 3 km / hr , how many seconds will he take to cover 90 meters ?
"the speed of the boat downstream = 15 + 3 = 18 km / hr 18 km / hr * 5 / 18 = 5 m / s the time taken to cover 90 meters = 90 / 5 = 18 seconds . the answer is d ."
divide(90, multiply(add(15, 3), const_0_2778))