Theo, who is dieting, requires 2 food supplements: I and II. He can get these supplements from

Question:

Theo, who is dieting, requires 2 food supplements: I and II. He can get these supplements from two different products A and B, as given:
Supplement I II
Product A...............3..................2
Product B...............2..................4
Theo's physician has recommended that he include at least 15grams of each supplement in his daily diet. If product A costs $.25 per serving and product B cost $.40 per serving, how can he satisfy his requirements most economically?