How many millions of U.S. viewers watched the episode that first aired on March 31, 2013?
CREATE TABLE "table1_11111116_8" (
  "no_in_season" real,
  "no_in_series" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "u_s_viewers_million" text
);
SELECT "u_s_viewers_million" FROM "table1_11111116_8" WHERE "original_air_date"='March 31, 2013';