This is a question about the volume of cylinders and cones. Take away the cone, and the water in the cup will fall, and the volume of the falling water is equal to the volume of the cone.

So, the answer is:

1, volume of cone: (6÷2)? ×3. 14×20÷3 = 188.4(cm？ )

2. Bottom area of cylinder: (20÷2)? ×3. 14=3 14(cm？ )

3. The water level drop height: 188.4÷3 14=0.6 (cm).

You got it? Come on!