Two important ingredients for baking bread are yeast and flour. To make a loaf of bread of at most 30 servings, maintain a yeast to flour ratio of 1:200. If you're making a loaf of more than 30 servings, use a ratio of 1:180. If you're making 30 servings of bread and using 0.45 oz of yeast, how many ounces of flour do you need? If you're making 90 servings of bread and using 720 oz of flour, how many ounces of yeast do you need?