1. **State the problem:** We need to find the constant of proportionality for a taxi service that charges a constant rate per mile, given the total cost for different miles traveled. 2. **Identify the formula:** The cost is proportional to the miles traveled, so we use the formula: $$\text{Cost} = k \times \text{Miles}$$ where $k$ is the constant of proportionality (rate per mile). 3. **Use the data:** From the table, for example, when miles = 2, cost = 6. 4. **Calculate $k$:** $$k = \frac{\text{Cost}}{\text{Miles}} = \frac{6}{2}$$ 5. **Simplify the fraction:** $$k = \frac{\cancel{6}}{\cancel{2}} = 3$$ 6. **Interpretation:** The constant of proportionality is 3, meaning the taxi charges 3 dollars per mile. 7. **Check with other data points:** For miles = 4, cost = 12, and $\frac{12}{4} = 3$, confirming the constant rate. **Final answer:** The constant of proportionality is $3$, which corresponds to option C: $\frac{3}{1}$.