I suggest to watch following video -https://www.youtube.com/watch?v=yIMMy8hh0WQDifference between Payback ROI NPV IRR and how do you apply in Project Management and please give examples which one to choose for the customer and what questions do we ask them to determine which one to use .
If something is not clear after watching above video, let's discuss
Note - PMI-PBA just needs a basic understanding of these concepts. Exam is neither going to ask these concepts in detail nor they will expect any understanding of calculations.