Awater tank has a mass of 3.64 kg when it is empty and a mass of 51.8 kg when it is filled to a certain level. what is the mass of the water in the tank?

Mass of empty water tank is 3.64 kg. Some amount of water is filled into the empty water tank. After filling of water upto certain level, the mass of the water tank becomes 51.8 kg. Mass of empty water tank + Mass of water = 51.8 kg. Hence, Mass of water present in the tank is equal to  difference in the mass of water tank with water and mass of the empty water tank.

Hence of mass of water filled in the tank is equal to  (51.8 - 3.64) kg =48.16 kg.