your next activity will update on 7 june then again on 21 june and so on after every 14 days.
How do you count that? One more mistake!
To explain that situation:
here is just one option:
His account till today earn 28 activity points + 35 posts.
Today his account is upgraded of 14 activity points.
Potential activity is 42 activity points.
In next two weeks you can upgrade your account up to max 42 activity points - you just need to write 7 posts.
It is not possible to exceed this limit, or speed it up.