We have the following:
[tex]d=\frac{m}{v}[/tex]now,
[tex]\begin{gathered} v=l^3 \\ v=3^3 \\ v=27 \end{gathered}[/tex]The volume is 27 cm^3. replacing:
[tex]\begin{gathered} d=\frac{81}{27} \\ d=3 \end{gathered}[/tex]The density is equals a 3 g/cm^3