The volume is V=399.48 m to the power of three
A unit rate simply means how many of one type of units you get per 1 other type of unit.
Examples of that:

This is rate of fluid flow of some pump for example. It pumps 300 liters every second.
Other example:

This is example for speed. Somebody is moving at 50 kilometers per hour (every hour he travels 50 kilometers)
Answer:
This circumference of the pond is 2πr (or 2π48), which equals 301.44m(assumine pi is 3.14). How long it takes to walk around depends on the rate of speed.
C. The temp at 10pm was 6°C. Over the next 3 hours, the temp dropped 2°C/hr.
6 -2(3) = 0