To calculate the volume of the cube we have to use the formula,
[tex]\rho = \frac{m}{V}[/tex]
Here, [tex]\rho[/tex] is the density , m is mass and V is the volume.
Given, [tex]\rho= 2.70 g/cm^{3}[/tex] and [tex]m = 2.1 kg[/tex] ( in gram [tex]m= 2.1 \times 1000= 2100 g[/tex])
Substituting the given values in above formula we get,
[tex]2.70g/cm^3 = \frac{2100 g}{V}[/tex]
or
[tex]V=\frac{2100 g}{2.70 g/cm^3}[/tex]
[tex]V= 777.8 cm^3[/tex]
Thus, the volume of cube is [tex]777.8 cm^3[/tex]