Facebook Inc. quickly concluded it wasn't worth anywhere near the $15 billion market value implied in a 2007 investment made by Microsoft Corp., according to confidential information obtained Wednesday from court documents. In a transcript of a June court hearing that was closed to the public, lawyers arguing over a legal settlement revealed Facebook's own appraisal had priced its privately held stock at $8.88 per share, giving it a market value of about $3.7 billion. The Palo Alto-based company relied on the appraisal to value employee stock options fairly and avert possible tax problems. Facebook, which runs the Internet's largest social network, made the assessment after striking an October 2007 deal with Redmond, Washington-based Microsoft. As part of a broader advertising partnership with Microsoft, Facebook agreed to sell a 1.6 percent stake to the software maker for $240 million.