The volume of a frustum of a cone is found by:

V = pi/12xhx(D^2+d^2+Dd)

Where h = height, D = major diameter, d = minor diameter

I have an upside down cone frustum (i.e. larger diameter at top) with known values for D, d and h.

The solid is half full of liquid (by volume). How do I find the height of the liquid?