The density of an object is by definition its mass over its volume.
[tex]\rho = m/V[/tex]
In the International system it has units of
[tex]\ \textless \ \rho\ \textgreater \ =kg/m^3[/tex]
Thus the density of the given object is
[tex]\rho =80(grams)/40(mL) = \frac{80*10^{-3}(kg)}{40*10^{-6}(m^3)} =2000 (kg/m^3)[/tex]
because [tex]1(gram)=10^{-3} (kg)
[/tex]
and
[tex]1 mL =10^{-3} (Liter) =10^{-3} (dm^{3}) =10^{-6} (m^3)
[/tex]
