I’m getting 6.7l/100 km using Google. Not sure what math you’re doing. But keep in mind there are two different gallons, US and Imperial or something. 35 mpg is pretty normal for a gasoline-only car these days (hybrids can do better depending on driving conditions - if they can spend most of their time on battery, for example). Diesel cars aren’t much of a thing in the US, again, especially after the whole Volkswagen cheating thing.

I know there used to be diesel cars in the 80s that would get crazy numbers like 50 mpg (4.7l/100km), and gas-powered cars probably could now, too, but emissions and safety requirements have pretty much killed that.