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_15681686_4 (rank__week_ VARCHAR, viewers__millions_ VARCHAR)
### Question:
what rank has viewers at 6.45?
### Answer:
SELECT rank__week_ FROM table_15681686_4 WHERE viewers__millions_ = "6.45"