99kg of water.
Since 100kg of mass = 66kg of water, all you have to do to find a mass of 60 is divide by 2 giving you 50kg of mass, and 33 kg of water. Then add that up onto 100kg of water and 66kg of water to get 150kg of mass and 99kg of water.
Hope this helps you, and have a nice day.
-R3TR0 Z3R0