If you've ever been in the car with your parents when they had to stop for gas, you may have heard them complain about the price. The average price of gas in the United States hit $4 a gallon last Friday, getting close to the all-time high of $4.11 a gallon from July 2008. The price of gas rises and drops based on factors such as demand and the price of crude oil. Different tax levels lead to different prices for gas in different states. Currently, the city with the highest average price of gas is Chicago, Illinois, at $4.50 a gallon. Tucson, Arizona, has the lowest average price, at $3.62 a gallon. How much more would it cost to fill a 12-gallon tank in Chicago than Tucson?