求救~　这个题目什么意思啊

这个题目不明白啊

  A family made a down payment of $75 and borrowed the balance on a set of encyclopedias that cost $400.The balance with interest was paid in 23 monthly payments of $16 each  and  a final payment of $9.The amount of interest paid was what percent of the amount borrowed?

我知道做法应该是23 X 16 +9 =377

377-(400-75)=52

52/325=0.16就是答案了

但是为什么the amount borrowed是400-75而不是400呢?$75payment是什么意思啊?谁能给我说说这个题目的大意呢?小女子是新手,问的大概比较白痴,还请大家多多原谅,将不胜感激~

在此谢过了!!

原文意思：买套百科问书$400，首期付$75，剩下的借。借款分23个月，每月还$16，最后好要还$9。问利息。计算较简单：共借400-75=325，共还23*16+9=377。所以利息为（377-325）/325=0.16

哦，原来是这样啊

谢谢拉