The force with which an object immersed in a tank of water is pushed out does not depend on the mass of the object. It is dependent only on the volume of the object. The buoyant force that pushes the object in the outwards direction is equal to the weight of water displaced.
A circular ball of radius r has a volume given by (4/3)*pi*r^3. Here r = 20 cm, the volume of the ball is (4/3)*pi*0.2^3 = 0.0335 m^3. As the density of water is not given the value at a temperature of 4 degree Celsius is being taken. The density of water at this temperature is of 1000 kg/m^3. The weight of the water displaced is 1000*0.0335*9.8 = 328.4 N
The buoyant force acting on the ball that pushes it out is equal to 328.4 N.