A dealer wishes to purchase a number of fans and sewing machines. He has only Rs. 5,760, to invest and has a space for at most 20 items. A fan cost him Rs.360 and a sewing machine Rs.240. His expectation is that he can sell a fan at a profit of Rs. 22 and a sewing machine at a profit of Rs. 18. Assuming that he can sell all the items that he can buy, how should he invest his money in order to maximise his profit ? Formulate this as a linear programming problem and solve it graphically.