can we insert photo here from question? (stepped fix costs)

hi!
I have a question which I do not understand and I can’t rewrite it here,- because it contains a lot symbols!
It is in Becker F2 book page 3-13
Ilustration 4 about stepped fixed costs.
Here is book
https://tiny.cc/s7m2cz

I have always thought I know all about high low method and stepped costs.
i have completed few questions and they all been right,- but I have no idea about this table.

I would just remove 10% of the highest and do traditional “high low method”…

***I dont understand what he means by numbers 1.1a ( what does even 1.1 stands for?)

*** where did 9920 came from?

Can anyone explain me what is happening in that table?

Thank YOU!!!