Newbie question. Riddle me this: The bag of scratch I have claims a minimum of 7.5% protein. It is made of three grains; cracked corn, red wheat, and milo. Wheat is about 12-13% crude protein. Cracked corn is 8-9%. And milo is about 10%. What proportions of these three grains would you have to mix to arrive at a protein level of 7.5%?