There are quite a few websites that have factor lists. Also, if you can find the biggest number that goes into it, then all of the factors of that number go into it as well.
Answer:
![r=\sqrt[3]{\frac{3V}{4\pi}}](https://tex.z-dn.net/?f=r%3D%5Csqrt%5B3%5D%7B%5Cfrac%7B3V%7D%7B4%5Cpi%7D%7D)
Step-by-step explanation:

We need to isolate 'r'
To isolate 'r' , first multiply by 3 on both sides
divide by 4pi on both sides

Take cube root on both sides
![\sqrt[3]{\frac{3V}{4\pi}}= r](https://tex.z-dn.net/?f=%5Csqrt%5B3%5D%7B%5Cfrac%7B3V%7D%7B4%5Cpi%7D%7D%3D%20r)
Act like it's a whole circle and find the perimeter, then divide by 2.
P = 2 * pi * r
P = 2 * 3.14 * 9
P = 56.52
Now divide by 2:
P = 28.26