Four foods x1,x2, x3, and x4 are to be produced. x1 contains 2 calories, no vitamin, and costs p40 per unit. x2 contains no calorie, 2 units of vitamins, and costs p100 per unit. x3 contains 1 unit of calorie, 1 unit of vitamin, and costs p120 per unit. x4 contains 3 units of calories, 2 units of vitamins, and costs p150 per unit. the minimum calorie requirements is 15 units and the minimum vitamin requirements is 8 units. how much of each food should be produced to satisfy these requirements and to minimize the total cost