I am trying to figure out how to get the answer, I don't want the answer just to know how to get it but I think that there is information missing.

Ok so it said that the paid invoice less the 2% discount and may 3rd return of 798 but I don't know how to get the paid invoice amount to find the answer. Please anyone give me guidance

Find the original invoice amount, subtract the return from May 3rd. That is how much is now due. The discount is for paying early, so the discount is only taken on the amount you're actually paying on. Since there was a return, you would not be paying on that portion. So you have to reduce by the return first, to see how much is now due and payable. And then figure your discount on that amount.