One big ball and four small balls discharge 24ml of water, one big ball and one small ball discharge 12ml of water, and 24ml is reduced 12ml, which is equivalent to one big ball minus one big ball and four small balls minus one small ball. Then, the water discharged by three balls is 12ml, and the water discharged by one ball.

24- 12= 12

12 divided by 3=4

12-4=8