user: Question: Result of W 21–7 had what average week?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Record', 'Game Site', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'real']
Sample row: [1.0, 'September 27, 1959', 'Detroit Lions', 'W 21–9', '1–0', 'Memorial Stadium', 55588.0]
SQL:

assistant: SELECT AVG("Week") FROM "Table" WHERE "Result" = 'W 21–7';