A sporting goods manufacturer is developing the production schedule for two types of tennis racquets. An order has been received for 180 of the standard model and 90 of the professional model. These are to be delivered at the end of this month. Another order has been received for 200 of the standard model and 120 of the professional model, but these are not to be delivered until the end of next month. Production in each of the two months may be in normal time or overtime. In the current month, a standard racquet may be produced at a cost of $40 on normal time, and a professional model may be purchased at a cost of $60 on regular time. Overtime raises cost of these to $50 and $70. Due to a new labor contract for next month, all costs will increase by 10% at the end of this month. The total number of racquets that may be produced in a month on regular time is 230, and an additional 80 racquets may be produced using overtime each month. Given the large order for delivery at the end of next month, the company is considering producing some extra racquets this month and keeping them in storage until the next month. The cost for keeping these in inventory for one month is estimated to be $2 per racquet. Formulate this as an LP problem to minimize cost.