Six college roommates have decided to make bracelets and necklaces as a way of paying down their student loans. They have made an arrangement with a local wholesale jeweler who will deliver 9,000 grams of metal to them each week. According to their designs, it will take 120 grams to make each necklace and 90 grams to make each bracelet. It takes an hour to make a necklace and a half hour to make a bracelet. Since they are all attending classes, the most they can collectively commit to this part-time job is 60 hours per week. They know from their research that they can make a profit of $30 on each necklace and $18 on each bracelet. How many necklaces and bracelets can they produce each week to maximize their profit?