18. Raturi and Rao, Inc., produces four industrial chemicals with variable production costs of $9.00, $6.75, $5.25, and $7.50 per pound, respectively. Because of increasing supplier costs, the variable cost of each of the products will increase by 6% at the beginning of month 3. Demand forecasts are shown in the following table. There are currently 100 pounds of each product on hand, and company wants to maintain an inventory of 100 pounds of each product at the end of every month.

The four products share a common process that operates two shifts of 8 hours each per day, 7 days per week. Processing requirements are 0.06 hours/pound for product 1, 0.05 hours/pound for product 2, 0.2 hours/pound for product 3, and 0.11 hours/pound for product 4. The per-pound cost of holding inventory each month is estimated to be 12% of the cost of the product. Develop an optimization model to meet demand and minimize the total cost. Implement your model on a spreadsheet and find an optimal solution with Solver.

Product Demand Product Month 1 Month 2 Month 3 1 1,000 800 1,000 2 1,000 900 500 3 600 600 500 4 0 200 500