CREATE TABLE table_5276 ("Club" TEXT, "Sport" TEXT, "League" TEXT, "Titles" FLOAT, "Founded" FLOAT)

Which Founded has a League of women's flat track derby association, and a Club of omaha rollergirls?
SELECT AVG("Founded") FROM table_5276 WHERE "League" = 'women''s flat track derby association' AND "Club" = 'omaha rollergirls'
SELECT AVG("Founded") FROM "table_5276" WHERE "Club" = 'omaha rollergirls' AND "League" = 'women\'s flat track derby association'