The calculated distance (air line) between Ganghwa-gun and Pyeongtaek is approximately 62 miles respectively 99 kilometers.
By car or train, the actual journey to Pyeongtaek is certainly longer, as only the direct route (as the crow flies) between Ganghwa-gun and Pyeongtaek has been calculated here.
Air line (approximately)
99 kilometers
54 nautical miles