Aresearcher 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 33.65 units of niacin and 38,700 units of retinol. she uses two types of commercial pellet foods. food a contains 0.11 unit of niacin and 195 units of retinol per gram. food b contains 0.38 unit of niacin and 75 units of retinol per gram. how many grams of each food does she feed this group of rats each day?