The calculated distance (air line) between Kangdong-ŭp and Haeju is approximately 79 miles respectively 127 kilometers.
By car or train, the actual journey to Haeju is certainly longer, as only the direct route (as the crow flies) between Kangdong-ŭp and Haeju has been calculated here.
Air line (approximately)
127 kilometers
68 nautical miles