Distance could be anything between 186.5 and 187.5

Petrol used could be anywhere between 27.5 and 28.5

So, best petrol consumption would be 187.5/27.5 = 6.818,

worst would be 186.5/28.5 = 6.543

The best that you can say then, is it's 6.68 + or - 0.14 (approx).