Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_91 (retired VARCHAR, notes VARCHAR)
### Question:
What year was the aircraft retired when it was replaced by 737-300s?
### Answer:
SELECT retired FROM table_name_91 WHERE notes = "replaced by 737-300s"