Two methods of weed control in an irrigation canal are under consideration. Method A involves lining at a cost of $4000. The lining will last 20 years. The maintenance cost with this method will be $3 per mile per year. Method B involves spraying a chemical that costs $40 per gallon. One gallon will treat 8 miles, but the treatment must be applied 4 times per year. In determining the number of miles per year that would result in breakeven, the variable cost for method B is closest to:
(a) $5 per mile
(b) $15 per mile
(c) $20 per mile
(d) $40 per mile