You haven't stated what units you would like the density to be shown in (usually it is kg/litre)
So density = mass/volume
density = 0.04kg/64cm^3 (64cm^3 came from 4cm x 4cm x 4cm) or if you want this in litres: 1000cm^3 = 1 litre, therefore: 1000/64 = 15.625 then multiply by 0.04 = 0.625kg/l
