Answer:
It costs $0.01 / mile less than before the mechanic worked on it.
Step-by-step explanation:
Cost to run the car before the mechanic worked on it:
[tex]4 * 8 = 32 dollars\\32 * 1/340 = 0.09 dollars/mile[/tex]
Cost to run the car after the mechanic worked on it:
[tex]4 * 7 = 28 dollars28 * 1/350 = 0.08 dollars/mile[/tex]
The difference between both cases is:
[tex]0.09 - 0.08 = 0.01 dollars/mile[/tex]