The calculated distance (air line) between Kosan and Hwangju-ŭp is approximately 89 miles respectively 144 kilometers.
By car or train, the actual journey to Hwangju-ŭp is certainly longer, as only the direct route (as the crow flies) between Kosan and Hwangju-ŭp has been calculated here.
Air line (approximately)
144 kilometers
78 nautical miles