how many millions of north american viewers had the episode whose director was Michael Lembeck? 
CREATE TABLE "table1_27714573_1" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code_s" real,
  "u_s_viewers_millions" text
);
SELECT "u_s_viewers_millions" FROM "table1_27714573_1" WHERE "directed_by"='Michael Lembeck';