By definition, density is mass per volume.
[tex]d=\frac{m}{v}[/tex]
Plugging in the given values gives:
[tex]d=\frac{78 g}{23 cm^3} =3.3913\frac{g}{cm^3}[/tex]
The only operation done in the problem is division, and both numbers have 2 significant figures, so this would be [tex]3.4\frac{g}{cm^3}[/tex] with correct significant figures.
