CREATE TABLE table_39993 ("Gill" TEXT, "Latitude" TEXT, "Longitude" TEXT, "Diameter  ( km ) " TEXT, "Diameter  ( mi ) " TEXT)

What shows for the Longitude when there is a Diameter (km) of 31km?
SELECT "Longitude" FROM table_39993 WHERE "Diameter (km)" = '31km'
SELECT "Longitude" FROM "table_39993" WHERE "Diameter (km)" = '31km'