The calculated distance (air line) between Yonggang-ŭp and Kaesŏng is approximately 87 miles respectively 139 kilometers.
By car or train, the actual journey to Kaesŏng is certainly longer, as only the direct route (as the crow flies) between Yonggang-ŭp and Kaesŏng has been calculated here.
Air line (approximately)
139 kilometers
75 nautical miles