A product can be produced on four different machines. Each machine has a fixed setup cost (incurred only if the machine is used), a variable production cost per unit processed, and a production capacity (see the table below). A total of 2000 units of the product must be produced. Formulate an IP whose solution will tell us how to minimize total costs.

Machine Fixed Cost Variable Cost per Unit Capacity
1 1000 20 900
2 900 25 1000
3 800 16 1100
4 700 30 2000