A researcher performs an experiment to test a hypothesis that involves the nutrients niacin and retinol. she feeds one group of laboratory rats a daily diet of precisely 37.08 units of niacin and 20,670 units of retinol. she uses two types of commercial pellet foods. food a contains 0.18 unit of niacin and 115 units of retinol per gram. food b contains 0.28 unit of niacin and 95 units of retinol per gram. how many grams of each food does she feed this group of rats each day?