CREATE TABLE table_31824 ("Week" FLOAT, "Date" TEXT, "Opponent" TEXT, "Result" TEXT, "Venue" TEXT, "Attendance" FLOAT, "Record" TEXT)

Tell mem the opponent for result of w 31-21
SELECT "Opponent" FROM table_31824 WHERE "Result" = 'w 31-21'
SELECT "Opponent" FROM "table_31824" WHERE "Result" = 'w 31-21'