1. **State the problem:** We need to find the density of a rock given its mass and volume. 2. **Formula:** Density ($\rho$) is defined as mass ($m$) divided by volume ($V$): $$\rho = \frac{m}{V}$$ 3. **Given values:** - Mass, $m = 210$ grams - Volume, $V = 70$ cm$^3$ 4. **Substitute the values into the formula:** $$\rho = \frac{210}{70}$$ 5. **Simplify the fraction:** $$\rho = \frac{\cancel{210}}{\cancel{70}} = 3$$ 6. **Interpretation:** The density of the rock is $3$ grams per cubic centimeter (g/cm$^3$). This means for every cubic centimeter of the rock, it has a mass of 3 grams.