The calculated distance (air line) between Sangsŏng-ni and Kaesŏng is approximately 85 miles respectively 136 kilometers.
By car or train, the actual journey to Kaesŏng is certainly longer, as only the direct route (as the crow flies) between Sangsŏng-ni and Kaesŏng has been calculated here.
Air line (approximately)
136 kilometers
74 nautical miles