Помогите пожалуйста

A:Are you going to watch this channel all evening?
B:No. I am going to switch off soon.Why?
A:There is a good film on.
It starts in 15 minutes.
Carole will come round to watch it with me.
B:Ok,when she arrives I will go upstairs and play computer games.
A:I am going to run in a marathon next year.
B:Really?You have to do a lot of training.
A:I know. I am going to run 5 km every day.
B:Wow!By the time you do the marathon
You will run about 1500 km.
A:That's right.Hey,you could do the marathon,too.
B: Oh,I am sorry.I will do something else that day.
A:But you don' t even know which day it is.
B:I know but,whatever day it is,I know I will not run in a marathon.