Weight of the solid in air (W1) = 1.5 kgf
Weight of the solid in liquid (W2) = 0.9 kgf
Density of the liquid = 1.2 × 103 kg m-3
RD of liquid = 1.2 × 10^3\over 1000 = 1.2
RD of solid = W_1\over W_1 - W_2 × RD of liquid
= 1.5\over 1.5 - 0.9 × 1.2
= 1.5\over 0.6 × 1.2
= 1.5 × 2 = 3