What was the attendance on September 11, 1988?
CREATE TABLE table_name_21 (attendance INTEGER, date VARCHAR)
SELECT AVG(attendance) FROM table_name_21 WHERE date = "september 11, 1988"
### Context: CREATE TABLE table_name_21 (attendance INTEGER, date VARCHAR) ### Question: What was the attendance on September 11, 1988? ### Answer: SELECT AVG(attendance) FROM table_name_21 WHERE date = "september 11, 1988"