How many viewers have an Air Date of march 20, 2008, and an 18-49 (Rating/Share) of 2.3/7?
CREATE TABLE "weekly_ratings" (
  "episode" text,
  "air_date" text,
  "timeslot" text,
  "rating" real,
  "share" real,
  "18_49_rating_share" text,
  "viewers_m" real,
  "rank_timeslot" real,
  "rank_night" text,
  "rank_overall" real
);
SELECT "viewers_m" FROM "weekly_ratings" WHERE "air_date"='march 20, 2008' AND "18_49_rating_share"='2.3/7';