Dan purchases a 25% interest in the Haymarket Partnership for $20,000 on January 1, 2010, and begins to materially participate in the partnership's business. The Haymarket Partnership uses the calendar year as its tax year. At the time of the purchase, the Haymarket Partnership has $2,000 in liabilities, and Dan's share is 25%. During the year, the Haymarket Partnership incurs $8,000 in losses and its liabilities increase by $4000. 

Required:

What is Dan's basis in his partnership interest on December 31, 2010?