According to the table,
maximum weight is in the air and minimum weight is in the salt solution due to minimum and maximum upthrust in the m respectively.
So A = air
B = salt solution
C = water
Weight of water displaced by the stone = 30 N -25 N = 5 N
Mass of water displaced = 5/10 kg
= 0.5 kg
Given ,
masss of 10 N stone is 1 kg.
So, mass of 30 N stone is 1/10 *30 Kg = 3 kg