What is the title of the episode directed by Christopher Petry with the production cod 3x6006?
CREATE TABLE "table1_26464364_1" (
  "no" real,
  "num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "u_s_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);
SELECT "title" FROM "table1_26464364_1" WHERE "directed_by"='Christopher Petry' AND "production_code"='3X6006';