Chemistry and Chemical Reactivity (9th Edition)

$7.99\ g/cm^3$
If the diameter is 9.40 mm, the radius (half of it) is $4.70\ mm=0.470\ cm$. The volume of the sphere is: $V=\frac43\pi r^3=0.435\ cm^3$ The given mass is 3.475 g, so the density is: $\rho=m/V=7.99\ g/cm^3$