Solution can be gained by using "Product of means = Product of extremes" concept. So the information we have is 23 miles on 1 gal and 135 mile on 'x' gal. 23 : 1 :: 135 : x As per Product of means = Product of extremes, 23 multiplied x = 135 multiplied by 1. And x will be 135 divided by 23 which is 5.86 gal Now, we have to convert gal to liters, 1 gal = 3.78 liters, so 5.86 gal = 5.86 multiplied by 3.78, which is 22.15 liters. Hence, 22.15 liters of gasoline are needed for a 135 mile trip