Carmichael's car used 8 gallons of gasoline to travel 340 miles after mechanic worked on the car it used 7 gallons of gasoline to travel 350 miles if the price of gasoline was approximately 4.00 per gallon. , how much less to the nearest cent per mile did it cost to run the car after the mechanic worked on it

Before the work was done, the cost was ...
  ($4/gal)*(8 gal)/(340 mi) = $32.00/(340 mi)

After the work was done, the cost was ...
  ($4/gal)*(7 gal)/(350 mi) = $28.00/(350 mi)

The savings is the difference of these costs:
  (32.00/340 -28.00/350) $/mi ≈ $0.01/mi

After the mechanic worked on the car, it cost about $0.01 per mile less to run.