According to the stem, when it is 6 cm above the water surface, the volume of water in the descending part is equal to the volume of a cylinder with a radius of 3 cm and a height of 6 cm. It can be concluded that the volume of water falling 7 cm is 3× 3× 3.14× 6 =169.56 cubic centimeters. According to the volume formula of the cylinder, it can be concluded that the bottom area of the water tank is 65438+. The volume of steel is equal to the volume of water after all steel is put into water 10 cm, so 24.22× 10=242.2 cubic cm.

Solution: The bottom area of the water tank is:

3. 14×32×6÷7≈24.22 (square centimeter),

The volume of steel is: 24.22× 10=242.2 (cubic centimeter).