In the original Western set-covering model in Figure 6.18, we assumed that each city must be covered by at least one hub. Suppose that for added flexibility in flight routing, Western requires that...

In the original Western set-covering model in Figure 6.18, we assumed that each city must be covered by at least one hub. Suppose that for added flexibility in flight routing, Western requires that each city must be covered by at least two hubs. How do the model and optimal solution change?