The formula with 35 substituted
L/100km = 235.214583 ÷ 35 = 6.72
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 35 mpg (US) is 42.03 mpg on the imperial gallon, 6.72 L/100km and 14.88 km/L. If your 35 mpg figure came from a British source it already uses the imperial gallon, and the metric answer is 8.07 L/100km instead.
What 35 mpg (US) means in practice
35 mpg is a strong figure for a non-hybrid petrol car and a common rating for compact sedans. At 6.72 L/100km it is the border between 'ordinary' and 'good' on European benchmarks too.