The formula with 22 substituted
L/100km = 235.214583 ÷ 22 = 10.69
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 22 mpg (US) is 26.42 mpg on the imperial gallon, 10.69 L/100km and 9.35 km/L. If your 22 mpg figure came from a British source it already uses the imperial gallon, and the metric answer is 12.84 L/100km instead.
What 22 mpg (US) means in practice
22 mpg (US) is what a good full-size pickup or a mid-size SUV with a V6 returns on the EPA combined cycle, and it is the single most searched mpg value for conversion to metric. It is 10.69 L/100km, and a hybrid version of the same vehicle would be around 8.