user: Question: What is the average Week when there were more than 63866 people in attendance on September 7, 1981?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [1.0, 'September 7, 1981', 'at Cleveland Browns', 'W 44–14', 78904.0]
SQL:

assistant: SELECT AVG("Week") FROM "Table" WHERE "Attendance" > 63866.0 AND "Date" = 'September 7, 1981';