The formula with 10 substituted
US gallons = 10 ÷ 3.785411784 = 2.642
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.
10 litres is 2.642 US gallons and 2.200 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 10 litres means in practice
10 litres is 2.642 US gallons or 2.200 imperial gallons, and is the amount a driver puts in when they want just enough to reach a cheaper station. In a 6 L/100km car it is good for 167 km, or about 104 miles.