What is the total when the B Score was 9.15 for Cheng Fei ( chn )?
CREATE TABLE "qualified_competitors" (
  "position" real,
  "gymnast" text,
  "a_score" real,
  "b_score" real,
  "total" real
);
SELECT AVG("total") FROM "qualified_competitors" WHERE "b_score"=9.15 AND "gymnast"='cheng fei ( chn )';