user: Question: Which Founded  has a League of Women's Flat Track Derby Association, and a Club of Omaha Rollergirls?
Columns: ['Club', 'Sport', 'League', 'Titles', 'Founded']
Types: ['text', 'text', 'text', 'real', 'real']
Sample row: ['Lincoln Stars', 'Hockey', 'US Hockey League', 5.0, 1996.0]
SQL:

assistant: SELECT "Founded" FROM "Table" WHERE "League" = 'Women''s Flat Track Derby Association' AND "Club" = 'Omaha Rollergirls';