On broadcast date is 25april1970, 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 "viewers_in_millions" FROM "table1_2102898_1" WHERE "broadcast_date"='25April1970';