Dear Bob,
This is Li Ming.I am writing to express my apology because I lost the book you lent mc last week.Last week,while I was reading in the library,I answered an emergency call and hurried to deal with an important matter.I was in such a hurry that I forgot to bring the book,and it had disappeared when I came back.It is my carelessness that resulted in such a situation.Therefore,I am willing to shoulder the responsibility.I decide to buy a new one as compensation,but I wonder whether it is acceptable to you.Please don't hesitate to tell me if you have better solutions,1 am willing to cooperate.I apologise again for the inconvenience I may bring.It would be highly appreciated should you take my letter into serious consideration.I am looking forward to your reply.
Yours sincerely,
Li Ming