The Cost of Gasoline 26) If 12 gallons of gas cost $16.68, then how much would 17 gallons of gas cost? 12 17 ----- = ----- 16.68 x 12(X) = 17(16.68) 12X = 283.56 X = 23.63 Let's now double-check by cross-multiplying: 12 * 23.63 = 17 * 16.68 283.56 = 283.56