Frederick's Feed company receives four raw grains from which it blends its dry pet food. The pet food advertises that each 8 oz. can meets the minimum daily requirements for vitamin C, protein and iron. The cost of each grain as well as the vitamin C, protein and iron are summarized below. Grain Vitamin C Units/lb Protein Units/lb Iron Units/lb Cost/lb
1 9 12 0 0.75
2 16 10 14 0.90
3 8 10 15 0.80
4 10 8 7 0.70

Frederick's is interested in producing an 8 oz. mixture at minimum cost while meeting the daily requirements of 6 units of vitamin C, 5 units of protein and 5 units of iron. Formulate this as a linear program: Assume 4 decision variables, x1,x2,x3 and x4.