I cann't make up the class at 18:45

Hi Liz,

I am really sorry to tell you that I won't be able to make up the class for you at 18: 45 of your time, as a new student will be arranged to me during that time.

So I can only call you at 18:15 or 18:30 except Friday and Saturday. Or do you want me to postpone the class for you?

Please let me know.