Gilda would do anything for Luna, her 11-year-old cat. Until recently, she had been paying an animal hospital $22.50 every weeks for a ten-pound bag of vitamin enriched organic cat food designed for older cats. On Wednesday, Gilda called a local pet store. The store stocks food similar to the one she buys at the animal hospital, but it is not organic. The store sells 25-pound bags for $59.55 and 50-pound bags for $99.50. Calculate the best buy among the three different-sized bags of cat food?