[求助]一道PREP数学题 我是不是昏了？

At a certain supplier, a machine of type A cost 20000d and a machine of type B costs 50000d, Each machine can be purchased by making a 20 percent down payment and repaying the remainder of the cost and the finance charges over a period of time, If the finance charges are equal to 40 percent of the remainder of the cost, how much less would 2 machines of type A cost than 1machine of type B under this arrangement?

10000

11200

12000

12800

13200

  da an shi 13200   wo zen me suan dou bu dui , wang jie da !

刚刚输入法有问题了  这道题具体意思是什么啊  我觉得自己理解了  但是做出来答案和上面的都不一样···

·····

我认为是：50-20×2+(50-20*2)*(1-20%)*40%=13200

LL是不是看漏了是两台A和一台B比？

我理解的是买台机器，先付款20%，再付剩下的80%+finance charges，而后者是剩下80%的40%