What is the date that a game at the Alltel Stadium had a final score of 6-20?
CREATE TABLE "1999" (
  "date" text,
  "visiting_team" text,
  "final_score" text,
  "host_team" text,
  "stadium" text
);
SELECT "date" FROM "1999" WHERE "stadium"='alltel stadium' AND "final_score"='6-20';