"Alrighty, so the distance from the Earth's surface to the Earth's core is 3,958 miles, and they traveled there in about 5 seconds.

This would be about 2,849,760 miles per hour.

That can easily be converted to mach speed if we divide it by the speed of sound in mph. Which would be around 767 mph.

The answer we'd get is Mach 3,715.4
Massively Hypersonic+"

- Credit to LeopoldTheBrave