CREATE TABLE table_1876825_6 (original_air_date VARCHAR2, production_code VARCHAR2)

What was the original air for the 06-03-521 production code?
SELECT original_air_date FROM table_1876825_6 WHERE production_code = "06-03-521"
SELECT "original_air_date" FROM "table_1876825_6" WHERE "06-03-521" = "production_code"