XYZ Company sells many household products through an on-line catalog. The company needs substantial warehouse space for storing its goods. Plans now are being made for leasing warehouse storage space over the next 5 months. Just how much space will be required in each of these months is known. However, since these space requirements are quite different, it may be most economical to lease only the amount needed each month on a month by- month basis. On the other hand, the additional cost for leasing space for additional months is much less than for the first month, so it may be less expensive to lease the maximum amount needed for the entire 5 months. Another option is the intermediate approach of changing the total amount of space leased (by adding a new lease and/or having an old lease expire) at least once but not every month. The space requirement and the leasing costs for the various leasing periods are as follows:

Month Required Space lease period cost per sq.ft.

1 30000 1 $650

2 25000 2 $1000

3 40000 3 $1300

4 15000 4 $1550

5 50000 5 $1600

The objective is to minimize the total leasing cost for meeting the space requirements. (5 marks)

(a) Formulate a linear programming model for this problem.

(b) Solve this model using Excel.