[paxys]

Per quarter, not per year. That is also the average across all users, while only the power users (ones that make up a majority of the ad revenue) will pay for a subscription, so their ad value is a lot more than average.

[internetter]

If the average revenue per user is then 72$ per year, then, it follows that the appropriate price is 6$ a month, not 12$?

[paxys]

Read the second part of what I wrote. If every existing user was forced to subscribe then $6 would be appropriate. If only people who earn them $50/mo in ads end up subscribing (which is a lot more likely) then Facebook will lose money on this option.