Suppose i have this list and there other lists. I have here the field date limite that is supposed to be equal to the field date +type ESC ( a lookup). My problem is that i cannot 

 then i cannot use my lookup list to do the sum.

I want to know please i am novice on sharepoint, if somebody could tell me step by step how could i do it with the workflow, that is the first thing.

The second thing is that i want that when the person enter a date, in the formula below 

It calculates automatically the date limit and copy all the informations on the list and put it at a task with the limit of date execution= date limits.

Please, i need answers