看不懂前句到底啥意思

题目

看不懂前句到底啥意思
What amount will reduce the amount due on an invoice of $1904.18 by $1097.21 if the terms of invoice are 1/15,n/60 and the payment was made during the discount period.The payment amount is?
“What amount will reduce the amount due on an invoice of $1904.18 by $1097.21” 我到底要回答的是哪个数.

答案