80 * (1+1/6) * 20 * 20-20 * 20 * 80 =1400 (square centimeter) = the volume of the cone.

62.8/3.14/2 =10cm = cone radius1400/(10 *10) =14cm = cone height.

Answer = 14cm

The principle is that the increased water volume-the original water volume = the volume of the cone.

Cone volume in use *3/ cone bottom = height