The $9-a-share cash deal, worth $17.2 billion including acquired debt, will increase the footprint of Walgreens, the largest U.S. drugstore chain, by half. It will also improve its ability to negotiate for low drug prices and fend off rivals from Wal-Mart Stores Inc (WMT.N) to online pharmacies. The price represents a 48 percent premium to where Rite-Aid shares closed on Monday, the day before the agreement was signed, the companies said in a joint release.