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_57 (year_joined__or_joining_ INTEGER, city VARCHAR)
### Question:
What year did the team from City of Aurora join?
### Answer:
SELECT AVG(year_joined__or_joining_) FROM table_name_57 WHERE city = "aurora"