How many episodes were written by david j. north & janet tamaro?
CREATE TABLE "table1_27969432_3" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production" text,
  "u_s_viewers_in_millions" text
);
SELECT COUNT("original_air_date") FROM "table1_27969432_3" WHERE "written_by"='David J. North & Janet Tamaro';