Which Visitor has a Series of 2 – 1?
CREATE TABLE "western_conference_quarter_finals_vs_6_c" (
  "date" text,
  "visitor" text,
  "score" text,
  "home" text,
  "decision" text,
  "series" text
);
SELECT "visitor" FROM "western_conference_quarter_finals_vs_6_c" WHERE "series"='2 – 1';