A mining company owns two mines. These mines produce an 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?