Overwriting an output cell to cause a different calculation ?

Hi all - I hope somebody can assist me or point me in the right direction. To be honest I don't even know if this is possible.

I have 3 columns say A, B & C

In A I have a number
In B I have a percentage
In C I have output A*B

The idea is that the user adjusts B and then the output in C changes. However, I would also like the user to have the ability to adjust column C directly which in turn would adjust column B to the correct %.

In my head I'm thinking that I should use conditional formatting on column B to say something like IF A<>C then calculate C/A otherwise do nothing.
However, I'm also aware that by inputting into column C directly, the user will overwrite the calculation in there already which if they wanted to then change again could cause problems.

Can anybody offer any advice please ?