CREATE TABLE table_31021 ("Distance" TEXT, "Adelaide" TEXT, "Brisbane" TEXT, "Canberra" TEXT, "Melbourne" TEXT, "Perth" TEXT, "Sydney" TEXT)

How many listings under Melbourne has a distance at 15km?
SELECT COUNT("Melbourne") FROM table_31021 WHERE "Distance" = '15km'
SELECT COUNT("Melbourne") FROM "table_31021" WHERE "Distance" = '15km'