The final product of a firm has a requirement that it must weigh at least 150 kg. The two raw materials used in the manufacture of this product are A with a cost of Rs. 2 per unit and B with a cost of Rs. 8 per unit. Each unit of A weighs 5 kg and each unit of B weighs 10 kg. At least 14 units of B and not more than 20 units of A must be used. What quantity of raw material of each type should be used for each unit of final product so as to minimize cost? Pose the problem as an LPP and solve it by graphical method.