The company's long$-$range planning group developed forecasts of the anticipated annual demand at the distribution centers as follows:

The shipping cost per unit from each plant to each distribution center is as follows:

$$

What is the optimal set of plants to open?

$($b$)$ Using equation $13\mathrm{.}1,$ find a second$-$best solution. What is the optimal set of plants to open?

What is the increase in cost versus the best solution from part $($a$)?$