One day it rained 18mm somewhere, that is to say, a cylindrical container with a unit area at the bottom was used to receive the rain. It happens that the height of the rain is 18mm, and now it is a cone, both of which have the same volume, which can be listed as follows:

Cylinder volume = cone volume, that is, 1 *18 =1/3 *1* h, so the unit area is1and the height is expressed by H.

So h= 18*3=54 mm =5.4 cm.