The calculated distance (air line) between Shek O and Tuen Mun San Hui is approximately 21 miles respectively 34 kilometers.
By car or train, the actual journey to Tuen Mun San Hui is certainly longer, as only the direct route (as the crow flies) between Shek O and Tuen Mun San Hui has been calculated here.
Air line (approximately)
34 kilometers
18 nautical miles