How many millions of U.S viewers are there when the director is andy wolk?
CREATE TABLE "table1_29747178_2" (
  "series_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);
SELECT "u_s_viewers_million" FROM "table1_29747178_2" WHERE "directed_by"='Andy Wolk';