Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_14 (founded INTEGER, league VARCHAR, club VARCHAR)
### Question:
Which Founded  has a League of women's flat track derby association, and a Club of omaha rollergirls?
### Answer:
SELECT AVG(founded) FROM table_name_14 WHERE league = "women's flat track derby association" AND club = "omaha rollergirls"