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 260 tons of regular-grade and 480 tons of low-grade ore per week. The first mine produces 4 tons of regular-grade and 16 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 $6000 per hour, and the operating cost of the second mine is $30,500 per hour. The first mine can be operated no more than 35 hours a week, and the second mine can be operated no more than 24 hours a week. How many hours per week should each mine be operated to minimize the cost