Please help with this, 20p

  about 325

Step-by-step explanation:

On average, the mileage is about 21.7 miles per gallon, so 15 gallons would be good for about 325 miles.

If we look at the table for fills that total 15 gallons, we see the first and last total 330 miles, and the 3rd and 4th total 314 miles. So, we expect somewhere between these values, on average.

A formal average adds the miles driven and divides by the total of gallons used. That result is shown below. While we might estimate that we could drive 325 miles on 15 gallons, we have found that our mileage actually varies.