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_2923917_4 (melbourne VARCHAR, distance VARCHAR)
### Question:
How many listings under Melbourne has a distance at 15km?
### Answer:
SELECT COUNT(melbourne) FROM table_2923917_4 WHERE distance = "15km"