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_60 (quantity INTEGER, year VARCHAR, model VARCHAR)
### Question:
Name the sum of quantity for before 2011 model slf-230
### Answer:
SELECT SUM(quantity) FROM table_name_60 WHERE year < 2011 AND model = "slf-230"