CREATE TABLE table_29637 ("Season" CLOB, "Episodes" FLOAT, "Timeslot  (  EST  ) " CLOB, "Season premiere" CLOB, "Season finale" CLOB, "TV season" CLOB, "Rank" CLOB, "Viewers  ( in millions ) " CLOB)

When was the season finale that ranked 20th?
SELECT "Season finale" FROM table_29637 WHERE "Rank" = '20th'
SELECT "Season finale" FROM "table_29637" WHERE "Rank" = '20th'