The calculated distance (air line) between Sinmak and Kangdong-ŭp is approximately 51 miles respectively 82 kilometers.
By car or train, the actual journey to Kangdong-ŭp is certainly longer, as only the direct route (as the crow flies) between Sinmak and Kangdong-ŭp has been calculated here.
Air line (approximately)
82 kilometers
44 nautical miles