user: Question: Tell me the sum of week for result of L 24–21
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'September 9, 1990', 'at Kansas City Chiefs', 'L 24–21', '68,363']
SQL:

assistant: SELECT SUM("Week") FROM "Table" WHERE "Result" = 'L 24–21';