The calculated distance (air line) between Bonchamp-lès-Laval and Rennes is approximately 45 miles respectively 72 kilometers.
By car or train, the actual journey to Rennes is certainly longer, as only the direct route (as the crow flies) between Bonchamp-lès-Laval and Rennes has been calculated here.
Air line (approximately)
72 kilometers
39 nautical miles