a mining company owns two mines. these mines produce and ore that can be graded into two classes: regular grade and low grade. the company must produce at least 350 tons of regular-grade and 610 tons of low-grade ore per week. the first mine produces 5 tons of regular-grade and 17 tons of low-grade ore per hour. the second mine produces 20 tons of regular-grade and 10 tons of low-grade ore per hour. the operating cost of the first mine is $18,000 per hour, and the operating cost of the second mine is $10,000 per hour. the first mine can be operated no more than 54 hours a week, and the second mine can be operated no more than 27 hours a week. how many hours per week should each mine be operated to minimize the cost?
