Dear Caroline,
How are you??? Let me thank you for your last letter. I'm sorry I didn't answer earlier, but I was really busy. It was great to hear from you.
I'm writing to you because I have a problem. I can't spend next week with you. I must prepare materials and study to my A-level exam. Sorry for that. I feel terrible. So instead of this date, we can go skiing on 24 Januar 2008. What do you think about this date??
I will change our reservation in the youth hostel or you can invite somebody else to spend this weekend with you.
Well that's all for me now. Give my regards to your parents. Please answer me quickly. Have a great weekend.
Love and kisses,
XYZ