The calculated distance (air line) between Ganghwa-gun and Cheongju-si is approximately 95 miles respectively 152 kilometers.
By car or train, the actual journey to Cheongju-si is certainly longer, as only the direct route (as the crow flies) between Ganghwa-gun and Cheongju-si has been calculated here.
Air line (approximately)
152 kilometers
82 nautical miles