The calculated distance (air line) between Kangdong-ŭp and Ongjin is approximately 92 miles respectively 149 kilometers.
By car or train, the actual journey to Ongjin is certainly longer, as only the direct route (as the crow flies) between Kangdong-ŭp and Ongjin has been calculated here.
Air line (approximately)
149 kilometers
80 nautical miles