Food `F_1` contains 5 units of vitamin A and 6 units of vitamin B per gram and costs 20 p/gm. Food `F_2` contains 8 units of vitamin A and 10 units of vitamin B per gram and costs 30 p/gm. The daily requirements of A and B are at least 80 and 100 units respectively. Formulate the problem as a linear programming problem to minimize cost.