How many kilometers from Phnom Penh to Tay Ninh if you travel by land?
How many hours is the trip from Phnom Penh to Tay Ninh by land?
Google Maps has a way of showing this for you.
In this case, searching for directions between the two shows that it's approximately 179km-244km, depending on which highway/road you take. The fastest route is expected to take 3 hours 20, and the longest will be just over 4 hours.
At this point you could look at the routes and perhaps check on google images for scenery; one route may be nicer to travel. On the other hand if you're taking a taxi or public transport, you may not get that choice.