The main volume of the circle: 3. 14*6*6*20=2260.8, not 226.08.

The second one:

What is taken out is the volume of potatoes. The water hasn't changed, and the water level has dropped. What is missing is potatoes.

40*3= 120

The third question:

Cone diameter: 18.84/3. 14=6, radius 3.

Cone volume: 3.14 * 3 *1.5/3 = 3.14 * 4.5.

Original volume: 3.14 * r * r * 2 = 3.14 * 4.5, R*R=2.25, R= 1.5.