The calculated distance (air line) between Yangp'yŏng and Seonghwan is approximately 44 miles respectively 71 kilometers.
By car or train, the actual journey to Seonghwan is certainly longer, as only the direct route (as the crow flies) between Yangp'yŏng and Seonghwan has been calculated here.
Air line (approximately)
71 kilometers
38 nautical miles