The calculated distance (air line) between Alchevsk and Sievierodonetsk is approximately 36 miles respectively 58 kilometers.
By car or train, the actual journey to Sievierodonetsk is certainly longer, as only the direct route (as the crow flies) between Alchevsk and Sievierodonetsk has been calculated here.
Air line (approximately)
58 kilometers
31 nautical miles