Help : Debt Calculating (Sum and Sub)

Hello...

Please I want Someone fix it to me

for ex: I have 500 Dollars

Person 1 > 100$ Borrow
Person 2 > 100$ Borrow
Person 3 > 100$ Borrow

mine 200$

300$ borrow

How to make the last 300 dolllar sub or sum when someone Pay me back the money or I borrow money

please Help, I will explain more if one of you can't get it

Thanks
Best regards

please anyone help me