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_33 (attendance INTEGER, opponent VARCHAR, date VARCHAR)
### Question:
What was the attendance on 31 January 2009 when the opponent was Airdrie United?
### Answer:
SELECT AVG(attendance) FROM table_name_33 WHERE opponent = "airdrie united" AND date = "31 january 2009"