谁帮我解一道英文数学题

题目

谁帮我解一道英文数学题
Stan was supposed to subtract a small number from a big number.He added them instead. The difference in Stan's answer and the correct was 120.If the big number was 280 more than the small number, what was the product of the two numbers?

答案

原题翻译如下:
stan小朋友被要求用一个大数减去一个小数,可是他把这两个数加起来了,结果加起来后,得数和正确答案相差120,如果大数比小数多280,那么这两个数的乘积是多少呢?
解题如下:
设小数是x,大数就是280+x,合是280+x+x,差是280+x-x,合减差等于120,所以280+x+x-（280+x-x）=120,解得x=60,所以小数是60,大数是340,两数相乘就是20400.