What is the average Episode Number, when Original Airdate is March 21, 2010, and when Season is less than 3?
CREATE TABLE "writer" (
  "year" real,
  "show" text,
  "season" real,
  "episode" text,
  "episode_number" real,
  "original_airdate" text
);
SELECT AVG("episode_number") FROM "writer" WHERE "original_airdate"='march 21, 2010' AND "season"<3;