B The volume of water is 40 * 40 * 30 = 48,000ml.
Solution: suppose you want to give Xml water:
(8000+x):(20 * 20)=(48000-x):(40 * 40)
20x= 192000- 128000
20x=64000
x=3200
3200ml = 3.2L.
Answer: It takes 3.2 liters of water from container B to container A. 。