Luis is an instructor at the Harrisonburg Automotive Mechanic School, where he leads the program in charge of automotive technicians. Currently, Luis is trying to arrange for the restoration of a couple of 1950's cars of his own, he has already acquired all the spare parts and materials needed, and now he's trying to arrange for labor. He can contract with any recently graduated student from the school at $10 per hour, or unlimited hours from a professional restoration mechanic at mix of three sources for help: unlimited hours from a promising current student of his at $4 per hour, up to 500 hours from a $25 projects, Luis estimates that the recent graduate is 0.3 as productive, and that his current student is 0.2 as productive. Luis has only 164 hours of his own time to devote to the effort, and he knows from experience that current students require more supervision than recent graduates, and recent graduates more than professional restorers. In particular, estimates that he will have to invest 0.2 hours