1818.9 miles
To find how many miles can be drove with one gallon, divide 348.3 by 9. This should get you 38.7 mpg.
Since it already provides how many miles can be driven my 40, I’m just going to multiply 38.7 by 7 and add it to the 40.
38.7 x 7 = 270.9
270.9 + 1548 = 1818.9