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. 。