The formula with 60 substituted
US gallons = 60 ÷ 3.785411784 = 15.850
The constant is an exact definition, not a rounded factor: the mile is 1.609344 km, the US gallon is 3.785411784 litres and the imperial gallon is 4.54609 litres. The Litres to Gallons Converter explains where each comes from and gives a longer table.
60 litres is 15.850 US gallons and 13.198 imperial gallons. The imperial gallon is 4.54609 litres against the US gallon's 3.785411784, which is why the two answers differ by a fifth.
What 60 litres means in practice
60 litres is 15.850 US gallons or 13.198 imperial gallons, a common tank size for mid-size sedans and SUVs in Europe. Filling it from empty at 1.70 a litre costs 102, which is the kind of sum that sends people looking for a fuel economy converter.