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_89 (year INTEGER, chassis VARCHAR)
### Question:
What year was the brabham bt46 bt48 bt49 Chassis common?
### Answer:
SELECT AVG(year) FROM table_name_89 WHERE chassis = "brabham bt46 bt48 bt49"