Counting occurrences within a timeframe

Hi,

I have attached a data file with a list of people who have bought weekly or annual passes ("A" or "W"). I want to know how to count how many monthly passes would have been sold if monthly passes were offered instead of weekly or annual passes. To do this, I would assume that any weekly passes that were bought would have been monthly passes and the next pass bought would be the earliest weekly pass bought that's bought at least a month after.

Thanks in advance for any help.

Data.xlsx