Dear Mr Cooper,
I work at the Friendship Bookstore on Dongfang Road where you often come to buy other day when you bought a dictionary at our bookstore I made a mistake abut the looked at two different editions of the same dictionary,one costing 30 yuan and the other 21 took the 21-yuan but I accepted 30 yuan from you.I didn't find out my mistake until you had you please come to the bookstore to get your change or to return your dictionary and get a 30-yuan edition instead? I apologize for whatever trouble this is causing you.
Yours truly
Li Hua