1. **State the problem:** A car travels 129.5 km using 9 L of gas. We want to find how far it can go with 50 L of gas at the same rate. 2. **Formula used:** Distance traveled is proportional to the amount of gas used. The rate (distance per liter) is given by: $$\text{Rate} = \frac{\text{Distance}}{\text{Gas}}$$ 3. **Calculate the rate:** $$\text{Rate} = \frac{129.5}{9}$$ 4. **Find the distance for 50 L:** $$\text{Distance} = \text{Rate} \times 50 = \frac{129.5}{9} \times 50$$ 5. **Simplify the expression:** $$\frac{129.5}{9} \times 50 = \frac{129.5 \times 50}{9}$$ 6. **Calculate numerator:** $$129.5 \times 50 = 6475$$ 7. **Final distance:** $$\frac{6475}{9} \approx 719.44$$ km **Answer:** The car can go approximately 719.44 km on a full tank of 50 L of gas.