The formula with 36 substituted
L/100km = 235.214583 ÷ 36 = 6.53
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 MPG to L/100km Converter explains where each comes from and gives a longer table.
The same 36 mpg (US) is 43.23 mpg on the imperial gallon, 6.53 L/100km and 15.31 km/L. If your 36 mpg figure came from a British source it already uses the imperial gallon, and the metric answer is 7.85 L/100km instead.
What 36 mpg (US) means in practice
36 mpg (US) is 6.53 L/100km and is what the best conventional compact cars achieve on the EPA cycle. In imperial terms that is 43.2 mpg, which sounds far better than it is to a British reader.