Projecting Income over Time

Hi

I need to create the following but i am having trouble. I want to see what the income per months is for the next 24 months.
Data:
Price per month for the service: 49 Euro,
50Euro one time fee.
There is 1 new customer per week and On average assume a customer leaves after 8 months. (this is what i am having problems with. Is their a formula to do this or what is the easiest way to get a clear montly view

Calculate: Income per month for the next 24 months.

Someone have a idea?

Kind regards

Kevin