Dear Ella,
I am writing to make an apology to you for I lost your book that you lent me. I am terribly sorry for my fault,It wasn't my intention to lost it somewhere.
To make up for my mistake,I would like to buy another one as a token of my apology.If everything else fails,I will sent you money on books by express as soon as possible. Would you tell me which way that you think is doable?
Again,I deeply apologize for the problems my actions caused.I look forward to hearing from you.
Yours sincerely,
Wang Yu