OH CRAP!  I misread and thought the container was 12 cm high instead
of 16. So I'll let another tutor do it.  Maybe I'll come back and redo 
it later.




The volume of a cone is 

The radius of the top of the container is 6, since it is
half the diameter, 12.

The volume of the whole cone container = 

Let the radius of the cone of water = x

Since the height of the cone container is twice the radius, that
will be true for the cone of water, so the height if the cone of
water will be twice x, or 2x.

The volume of the cone of water = 

Since the volume of the cone of water is half the volume of the cone
container, the former equals twice the latter: 









Divide both sides by 4















I'm not sure what you mean by "how deep is the water?"

If it's the height of the cone of water it's = 2x = 9.524406312 cm.

If it's distance from the top of the container to the top
of the water it's 12 - 9.524406312 = 2.475593688 cm.

Round off as you were told.

Edwin