In a psychology experiment on conditioning, an experimenter places mice and rats into two types of conditioning boxes, I and II. Each mouse spends 20 minutes per day and each rat spends 40 minutes per day in box I. Each mouse spends 40 minutes per day and each rat spends 20 minutes per day in box II. Suppose box I is available to the experimenter for 640 minutes per day and box II is available for 800 minutes per day. How many rats and mice should be used to maximize the total number of animals in the experiment in a day?