Hi,
Work:
[tex]28miles = 1gallon[/tex]
To find the cost of gallons spend for 310 miles you need to first find the amount of gallons consumed on 310 miles path.
[tex]310 \div 28 = 11.07gallons[/tex]
If each costs 3.5$ you need to multiply gallons with money.
[tex]3.5 \times 11.07 = 38.745[/tex]
You would spend 38.745$ to drive 310 miles.
Hope this helps.
r3t40