user: Question: What is the attendance when the opponent is the San Francisco 49ers?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'September 9, 1990', 'at Atlanta Falcons', 'L 47–27', '56,222']
SQL:

assistant: SELECT "Attendance" FROM "Table" WHERE "Opponent" = 'San Francisco 49ers';