Problem 3: Modify the CPL model to take into account that a subset of already existing facilities V Vi cannot be closed (but can be upgraded). Indicate the current fixed cost and capacity of facility i e Vi as f; and qi', respectively. Moreover, let fi and qi" be the fixed cost and capacity if facility i e Vi is upgraded, respectively. The original CPL model is: Minimize , , + f, xy, ieli jeV2 iel = Subject to Ex, = 1, jeV jeV2 Ed, xx, 59, xy,,i e V, jeV2 where C;; = 7;, xd,, y; = 0,1, 0