Dear Margarita,
Thank you for asking me to babysit for you. As you know I enjoy looking after Anthony and would be happy to help you out. However, this weekend I have a commitment which I cannot break.
My parents are coming to visit and I am going to take them down to the coast as I have always promised to do. They are getting older so I like to spend as much time with them as possible. Also, it is my father's birthday and I want to celebrate with them. I am really sorry that I am not able to help this time, but I am free next weekend and I would be glad to babysit for you then, if you should choose to go out for the evening.
My charge is fifteen dollars per hour until midnight and twenty dollars per hour after that. You would need to give me any special instructions you might have and, of course, leave a phone number in case of emergency.
Yours sincerely,
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