Final answer:
The density of the brown sugar is 1.61 g/cm³.
Step-by-step explanation:
The density of a substance is calculated by dividing its mass by its volume. In this case, the mass of the 8 cubic centimeter block of brown sugar is 12.9 g. To find the density, we divide the mass by the volume:
Density = mass / volume
Density = 12.9 g / 8 cm³ = 1.61 g/cm³
Therefore, the density of the brown sugar is 1.61 g/cm³.