A meat market combines ground beef and ground pork in a single package for meat loaf. The ground beef is 75% lean(75% beef, 25% fat) and costs the market $0.75 per pound(lb). The ground pork is 60% lean and costs the market $0.45 /lb. If the market wants to use at least 50 lb of its available pork, but no more than 200 lb of its available ground beef, how much ground beef should be mixed with ground pork so the cost is minimized? Show your work completely.