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 420 tons of regular-grade and 480 tons of low-grade ore per week. The first mine produces 6 tons of regular-grade and 16 tons of low-grade ore per hour. The second mine produces 18 tons of regular-grade and 8 tons of low-grade ore per hour. The operating cost of the first mine is $16,000 per hour, and the operating cost of the second mine is $ 12,800 per hour. The first mine can be operated no more than 55 hours a week, and the second mine can be operated no more than 36 hours a week. How many hours per week should each mine be operated to minimize the cost? Note that the ALEKS graphing calculator can be used to make computations easier. First mine: hour(s) Second mine: hour(s)