What is the original air date of the episode directed by Paul Marcus?
CREATE TABLE "table1_15026994_3" (
  "num" real,
  "episode" text,
  "writer" text,
  "director" text,
  "original_air_date" text,
  "viewing_figure" text
);
SELECT "original_air_date" FROM "table1_15026994_3" WHERE "director"='Paul Marcus';