How many million viewers watched the episode that aired on March 28, 2010?
CREATE TABLE "us_ratings" (
  "num" real,
  "airdate" text,
  "episode" text,
  "rating" text,
  "share" real,
  "rating_share_18_49" text,
  "viewers_millions" text,
  "rank_timeslot" real,
  "rank_night" real
);
SELECT "viewers_millions" FROM "us_ratings" WHERE "airdate"='March 28, 2010';