Density is mass per unit volume,
[tex]\rho=\dfrac mV[/tex]
so to get the volume, divide the mass by the density,
[tex]V=\dfrac m\rho[/tex]
So the volume is
[tex]\dfrac{210\,\mathrm g}{7.981\frac{\rm g}{\mathrm{cm}^3}}\approx26.312\,\mathrm{cm}^3\approx\boxed{26\,\mathrm{cm}^3}[/tex]
