Beth sold her 25% partnership interest to Katie for $50,000 cash on July 1 (the halfway point) of the current tax year. Katie also assumed Beth's share of the partnership's liabilities. Beth's basis in her partnership interest at the beginning of the year was $40,000, including a $15,000 share of partnership liabilities. The partnership's income for the entire year was $100,000, and Beth's share of partnership debt was $10,000 as of the date she sold the partnership interest. Assume the calendar year partnership has no hot assets, all of its income is earned evenly throughout the year, and the partnership uses the monthly proration method to allocate its income among the partners. Beth recognizes a gain of how much on the sale?