Which Score has an Attendance larger than 16,851, and an Away team of sheffield united?
CREATE TABLE "fifth_round_proper" (
  "tie_no" text,
  "home_team" text,
  "score" text,
  "away_team" text,
  "attendance" real
);
SELECT "score" FROM "fifth_round_proper" WHERE "attendance">'16,851' AND "away_team"='sheffield united';