$1)$ Use a level approach to develop an aggregate plan using the highest demand as the constant output rate per month. What is the total cost of this plan? $2)$ Use a chase approach to develop an aggregate plan. If the company wants to use the on$-$hand inventory as early as possible, what is the total cost of this plan? $3)$ Keep the initial workforce level constant and use overtime and subcontracting as needed. Production rates can vary, but no backorders, hiring, or firing are allowed. The inventory at the end of month $6$ is $40$ desks. What is the total cost of this plan?