Let's imagine you own a tennis club with two sources of revenue: one is the fee that people pay every year ($300 out of which the contribution margin is $200). Then people who come to the club spend on various things (balls drinks snacks). Contribution margin is $60. This is the M. Historically, 80% of the members rejoin each year. For the time being, let's look at a 4-year time horizon, then we'll expand. 

So, what is the expected profitability of an average customer? 

For simplicity, assume no interest rates. Let's calculate together, based on this information.