The density of the substance is what is asked in the question. It can be determined by dividing the mass of the substance by its volume. Since the mass of the substance is 6.48 g and the volume is 3 cm, we have:

$$d = \dfrac{m}{V} = \dfrac{6.48 \text{ g}}{3 \text{ cm}^3} = 2.16 \text{ g/cm}^3$$

Therefore, the density of the substance is 2.16 g/cm3, which means that for every cubic centimeter of the substance, it has a mass of 2.16 grams.