First, let's calculate the distance the car travels, using the formula:

Where speed is 65 miles/hr and time is 2.6 hrs:

Then, let's do the conversion from miles to kilometers:

Now, with this value, we can calculate the number of liters and gallons of gasoline that were used using the average gas use of 17.8 km/L, like this:

We can convert liters to gallons, like this:

The answer is that the trip uses 15.3 L which is the same that 4.04 gallons of gasoline.