Good Guys, an appliance retailer, is undergoing massive expansion in Australia. This has put significant pressure on its existing warehouses. As part of the companys long-term strategy, Good Guys is considering opening new warehouses in Melbourne, Sydney, Perth, and Brisbane. Each warehouse, when opened, can ship up to 135 units of appliance per week, and for economies of scale, there is a minimum shipping quantity of 20 units from each opened warehouse.

The weekly fixed cost for keeping each warehouse open is $500 for Melbourne, $600 for Sydney, $400 for Perth, and $350 for Brisbane. Region 1 of the country requires 100 units per week, region 2 requires 85 units per week, and region 3 requires 60 units per week. The costs (including production and shipping costs) of sending one unit from a plant to a region are shown below.

	Region 1	Region 2	Region 3
Melbourne	29	46	55
Sydney	52	19	30
Perth	30	38	21
Brisbane	28	54	39

Develop an integer linear programming model to help Good Guys meet weekly demands at a minimum cost, subject to the above information and the following restrictions:

• If the Brisbane warehouse is opened, then the Melbourne warehouse must be opened.
• Either the Melbourne or the Sydney warehouses must be opened.