CREATE TABLE table_20284 ("Episode" FLOAT, "Title" TEXT, "Story" TEXT, "Adapted by" TEXT, "Director" TEXT, "Airdate" TEXT, "Exists?" TEXT)

What is the airdate when the story is listed as hugh leonard?
SELECT "Airdate" FROM table_20284 WHERE "Story" = 'Hugh Leonard'
SELECT "Airdate" FROM "table_20284" WHERE "Story" = 'Hugh Leonard'