Walgreen Co. said it will expand its presence in Puerto Rico by acquiring 20 drugstores from Farmacias El Amal. Terms of the deal were not disclosed. Deerfield-based Walgreen began operations on Puerto Rico in 1960 and currently operates 73 stores there. It expects the acquisition to close during the 1st-Q and said family-owned El Amal will continue to run its 41 other stores in Puerto Rico. Walgreen