As monthly payments come in from Borrowers they adjust the FMV by subtracting the principal portion of the payment from the existing FMV (or at least some percentage of the principal).

You need to add/subtract the income and deductions within each "bucket" first. 

I know I need to find ARV by looking for comps in the area and if it needs work I can subtract rehab costs from the ARV to get a general idea of the highest offer price.Other than that, I’m struggling to find resources on how to learn real estate finance.

I am not sure what state you are in, but you might have excise tax on top of all the other fees.Then you have got subtract out what you owe.

Hello Would the capital gains tax happen on the amount after the mortgage is paid off and subtracted the initial invested fund?

I subtract our the condo fee from rent, and then measure against my buy criteria. 

I served them a warning last Saturday (1/30) requesting to clean up by Monday 2/1 or potentially hiring a cleaning company and subtracting the expense from tenant's security deposit.  

@Scott Benton reminds me of when I was in my twenties and instead of balancing my check book I wrote  checks to myself subtracted them from my balance and tucked  them away. 

@Dave FosterAdmittedly I didn't add/subtract every number provided... 

My all-in price for a century old duplex is 120, so I start there and subtract out all the repairs and that's what I'll go as high as in the negotiations.