The calculated distance (air line) between Pyeongtaek and Gyeongsan-si is approximately 122 miles respectively 197 kilometers.
By car or train, the actual journey to Gyeongsan-si is certainly longer, as only the direct route (as the crow flies) between Pyeongtaek and Gyeongsan-si has been calculated here.
Air line (approximately)
197 kilometers
106 nautical miles