user: Question: Tell mem the opponent for result of W 31-21
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Venue', 'Attendance', 'Record']
Types: ['real', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: [1.0, '1962-09-16', 'at Green Bay Packers', 'L 34-7', 'City Stadium', 38669.0, '0-1']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Result" = 'W 31-21';