Which Rank has Notes of fb, and a Time of 5:57.31?
CREATE TABLE "semifinal_a_b_1" (
  "rank" real,
  "athlete" text,
  "country" text,
  "time" text,
  "notes" text
);
SELECT "rank" FROM "semifinal_a_b_1" WHERE "notes"='fb' AND "time"='5:57.31';