A firm produces N products and has M production plants. The following data is available for aggregate production planning over T months: The cost of producing product i in plant j in month t is cijt. The holding cost per unit of product i in month t is hit. Each worker in plant j is paid gjt dollars in month t. The cost of hiring one worker in plant j is bj and the cost of firing one worker in plant j is rj. Producing one unit of product i in plant j require aij worker hours. The number of working hours in month t in plant j is njt. The demand for product i in month t is dit. Formulate an LP to find the aggregate production plan with minimum total cost.