work problem to pump liquid out of a tank

A tank in the shape of an inverted right circular cone has height 6 meters and radius 4 meters. It is filled with 4 meters of hot chocolate. Find the work required to empty the tank by pumping the hot chocolate over the top of the tank. The density of hot chocolate is http://math.webwork.rochester.edu:80...e00ebca4b1.png

I know how to do these problems.

find the volume of a slice and times 9.8 m/s^2 and by 1070kg, etc ect

but I keep getting the wrong answer.