A firm produces health supplements and makes the following demand forecasts in a 4-month period as in the table below. Demand refers to the quantities of product ordered by customers in a month, and days refer to the number of working days in a month. Month May Jun Jul Aug Demand (kg) 3,500 4,700 3,800 4,500 Days 21 22 22 22 The firm currently hires 9 workers in its production site. On average, one worker can produce 20kgs of product per working day. To adjust its production operations, the firm considers undertime and overtime. According to the firm's human resource policy, the maximum allowable undertime is equivalent to one (1) day per month per worker, while the maximum allowable overtime is equivalent to two (2) days per month per worker. On average, one (1) kg of product generates a revenue of $141. The average material cost of one (1) kg of product is $57. The average salary for a worker is $4,800/month. If overtime is used, the average overtime payment is $400 per day per worker. Unfulfilled demands are considered as backorders, and the estimated backorder cost is $380 per kg of product per month. Unsold finished products are stored in warehouse and incurs inventory holding cost of $56 per kg per month. The warehouse can accommodate a maximum of 350 kgs of finished product inventory. Assume that the initial inventory of finished product at the beginning of May is 200 kgs.