The dean of the Western College of Business must plan the school's course offerings for the fall semester. Students demands make it necessary to offer at least 30 undergraduate and 20 graduate courses in the term. Faculty contract also dictate that at least 60 courses be offered in total. Each undergraduate course taught cost the college an average of $2,500 in faculty wages, and each graduate courses cost $ 3,000. How many undergraduate and graduate courses should be taught in the fall so that the total faculty salaries are kept to a minimum?