Asubstance has a mass of 360 g and a volume of 7.5 cm3. what is its density?

Mass of the substance = 360 gm
Volume of the substance = 7.5 cm^3
Now we know that
Density = Mass/Volume
             = 360/7.5 gm/cm^3
             = 48 gm/cm^3
So the density of the substance given in the question is 48 gm/cm^3. . I hope that you have understood the procedure by which the density of any substance can be easily determined and also got the answer you were looking for. By following this method you can easily determine the density of any substance without requiring any help.

Answer is to avoid experimental error

The mass has escaped into a gas which you can not see so the law stays true.