Pick some easy numbers. Say S = 90, so we're covering 90km/hour. And we'll say that E = 30, so we're going 30 km/1 liter. (Which is the same as saying that 1 liter allows us to cover 30km.)

If we drive for one hour at 90km/hour, we'll cover exactly 90km. If we cover 90km, and 1 liter allows us to cover 30km, we'll use a total of 3 liters. Now check to see which expression gives us a value of 3. S/E = 90/30 = 3. Check S/E on the left

If we cover 60 km, and 1 liter allows us to cover 30km, we'll use 2 liters. 60/E = 60/30 = 2. Check 60/E on the right.