The calculated distance (air line) between Yŏnmu and Pyeongtaek is approximately 60 miles respectively 96 kilometers.
By car or train, the actual journey to Pyeongtaek is certainly longer, as only the direct route (as the crow flies) between Yŏnmu and Pyeongtaek has been calculated here.
Air line (approximately)
96 kilometers
52 nautical miles