So Kelly got 14 gallons of gas for 29.26. She is wondering how much it would be to fill it up to 17 gallons. So what you have to do is first find out how much the gas cost per gallon. so you would divide 29.26 by 14 to get 2.09. so now that you have how much it is per gallon all you have to do is multiply the amount per gallon {2.09} by 17. so when you multiply 2.09 by 17 you get 35.53. So Kelly had to pay 35.53 for a 17 gallon tank of gas!