The calculated distance (air line) between Hwangju-ŭp and Pyongyang is approximately 25 miles respectively 40 kilometers.
By car or train, the actual journey to Pyongyang is certainly longer, as only the direct route (as the crow flies) between Hwangju-ŭp and Pyongyang has been calculated here.
Air line (approximately)
40 kilometers
22 nautical miles