On broadcast date is 21march1970, how many people tuned in?
CREATE TABLE "table1_2102898_1" (
  "episode" text,
  "broadcast_date" text,
  "run_time" text,
  "viewers_in_millions" text,
  "archive" text
);
SELECT COUNT("viewers_in_millions") FROM "table1_2102898_1" WHERE "broadcast_date"='21March1970';