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_87 (founded INTEGER, coach VARCHAR, location VARCHAR)
### Question:
What is the average year that the club located in enfield was founded with an unknown coach?
### Answer:
SELECT AVG(founded) FROM table_name_87 WHERE coach = "unknown" AND location = "enfield"