Whats the density of the unknown liquid

A metal block when fully immersed in a liquid of density 4kg/litre loses 15 kg. The same object when fully immersed in an unknown liquid loses 27kg. Calculate the density of the unknown liquid.

Just Cross Multiply.

(Unknown Density) / (Mass lost in Unknown) = (Known Density) / (Mass Lost in Known)

(X) / (27kg) = (4kg/L) / (15kg)
15kg(X) = 108kg^2/L
X = (108kg^2/L)/ 15kg
X = 7.2kg/L

The density of the unknown liquid is 7.2kg / L

Density of the unknown liquid = d
Volume of block = V, so volume of liquid displaced =V

Mass of liquid displaced by block = density of liquid x volume of liquid

For 1st liquid
Apparent loss of weight = weight of liquid displaced.
15 = 4 x V
V = 15/4 litres

For 2nd liquid
Apparent loss of weight = weight of liquid displaced.
27 = d x V
= d x 15/4

d = 27x4/15 = 7.2 kg/litre