621 miles is how many hours?

Answer 1

That depends on how fast you are moving. Maybe you're in a car that's going at 65 mph, or maybe it's crawling along at 5 mph. Maybe you're sitting on the ground. The rate at which you are going decides how long it will take you to cover the same amount of distance.

Answer 2

This question cannot be answered sensibly. A mile is a measure of distance, with dimensions [L]. An hour is a measure of time, with dimensions [T]. Basic dimensional analysis teaches that you cannot convert between measures with different dimensions such as these without additional information, such as mode of transport.