Plastic-Fab Ltd is preparing its production plans for the coming month. It manufactures two types of plastic water storage tanks, Class A and Class B. Sales and production data, per unit of the storage tank, are as follows: Class A tank Class B tank Selling Price (RM) 205 125 Raw Material (kg) 6 4 Skilled labour (hour) 10 10 25 5 Semi-skilled labour (hour) The supply of raw materials is limited to 900kg per month, while the supply of skilled and semi- skilled labour is limited to 2000 hours and 2500 hours per month respectively. All water tank produced can be sold. Formulate a linear programming model to determine number of Class A and Class B water tanks that should be produced to maximize Plastic-Fab's total sales. Sketch a graph, identity the corner points and find the optimal solution for this problem. (14M)