Use IP to formulate and solve the following problem: A chain of stores has too many stores in close proximity. Specifically, the store numbers within each grouping are too close: (1,3), (1,2,4), (4,5,6), (6,9), (6,7,8), (8,10), (9,10). It only wishes to retain 7 stores, one within each of these groupings. The monthly profit from each store is given. The objective is to select the stores to retain to maximize overall profits. The profits of the stores are 12,15,18,10,9,18,12,13,11, and 8.