Staples announced yesterday that it has agreed to sell the company to private equity firm Sycamore Partners for $6.9 billion. Sycamore specializes in turning around retail companies and has previously taken over Talbot, Coldwater Creek and The Limited. With Staples, which runs 1,240 stores in the U.S., the firm will need to regain footing in a segment that has increasingly given ground to online sales.