4. A farmer has determined that each year, he needs to fertilize his field with at least 1200 pounds of calcium and at least 600 pounds of magnesium to yield the best harvest. Each bag of Brand X fertilizer contains 6 pounds of calcium, 2 pounds of magnesium and 1 pound of sulfur. Each bag of Brand Y fertilizer contains 3 pounds of calcium, 3 pounds of magnesium and 1 pound of sulfur. How many bags of each brand should be used to meet the minimum fertilizer requirements and also minimize the amount of sulfur added to the field? 4. A farmer has determined that each year, he needs to fertilize his field with at least 1200 pounds of calcium and at least 600 pounds of magnesium to yield the best harvest. Each bag of Brand X fertilizer contains 6 pounds of calcium, 2 pounds of magnesium and 1 pound of sulfur. Each bag of Brand Y fertilizer contains 3 pounds of calcium, 3 pounds of magnesium and 1 pound of sulfur. How many bags of each brand should be used to meet the minimum fertilizer requirements and also minimize the amount of sulfur added to the field