For the first one his car used 8/340 or 2/85 gallons for one mile.
After the fix, his car 7/350 or 1/50 gallons for one mile.
Then you subtract 1/50-2/85 to get (17-10)/850 or 7/850.
You multiply this by 4 to get 28/850 which is $0.0329411
Since it is asking for cents you multiply by 100 to get approximately 3 cents.
