Macro to fill only when there's value in cell B

Hi,

I would like to have a macro to have column N and O run the formula whenever there's a value or a change/update in column B.

I would also require the formula to run til the last found value in column B.

Sorry I have zero knowledge in VBA and I can only macro record and edit, but with this I can't do it as I want it to run without any hot key.

Attached is the sample file.

sample.xlsx

Thanks a lot in advance!