Which Visitor has a Home of calgary, and a Date of april 17?
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 "home"='calgary' AND "date"='april 17';