The calculated distance (air line) between Solothurn and Zürich (Kreis 9) / Altstetten is approximately 46 miles respectively 74 kilometers.
By car or train, the actual journey to Zürich (Kreis 9) / Altstetten is certainly longer, as only the direct route (as the crow flies) between Solothurn and Zürich (Kreis 9) / Altstetten has been calculated here.
Air line (approximately)
74 kilometers
40 nautical miles