Archimedes' principle

There is only one queation (Q(c) ) on Archimedes' Principle
At equilibrium,
mg + T = upthrust
where m is the mass of the object(= 800 kg), g is the acceleration due to gravity, T is the tension of the chain (= 1600 N)
hence, upthrust = (800g + 1600) N = 9600 N (taking g = 10 m/s2)
By Archimedes' Principle, upthrust = weight of water displaced
i.e. weight of water displaced = 9600 N
Mass of water displaced = 9600/g kg = 960 kg