Volume of a Spherical Shell

The volume of a spherical shell is the difference between the enclosed volume of the outer sphere and the enclosed volume of the inner sphere:

Create a function that takes r1 and r2 as arguments and returns the volume of a spherical shell rounded to the nearest thousandth.

Examples

vol_shell(3, 3) ➞ 0

vol_shell(7, 2) ➞ 1403.245

vol_shell(3, 800) ➞ 2144660471.753

Notes

The inputs are always positive numbers. r1 could be the inner radius or the outer radius, don't return a negative number.