Advice needed for optimal setup

Thanks emre i will read this tutorial very soon!
For the other problem i’ve tried to follow this thread

I’ve read a lot of thread about add tip on a ticket or a service charge based on a percentage of ticket amount but my case is a little different. I need to add an amount to the ticket based on the number of people sitting at a certain table. I have defined a ticket tag to store how many costumers are at the table and it splash to the screen when i select a table,


then i’ve set accounts, transaction type and calculation types but here i don’t know how to set it (fixed rate or custom or whatever else).

then i set action and rule:


i must only add to the ticket amount the ticket tag value multiplied by a fixed amount (1,50€) without any variation for other price reported in the ticket. I’m going crazy for something seemingly so simple

then the actual result: