What is the average year that the club located in enfield was founded with an unknown coach?
CREATE TABLE table_44897 (
    "Team" text,
    "Coach" text,
    "Home Ground" text,
    "Location" text,
    "Founded" real
)
SELECT AVG("Founded") FROM table_44897 WHERE "Coach" = 'unknown' AND "Location" = 'enfield'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: What is the average year that the club located in enfield was founded with an unknown coach? ### Input: CREATE TABLE table_44897 (
    "Team" text,
    "Coach" text,
    "Home Ground" text,
    "Location" text,
    "Founded" real
) ### Response: SELECT AVG("Founded") FROM table_44897 WHERE "Coach" = 'unknown' AND "Location" = 'enfield'