Summing a percentage of a list amount from one module to another

Here is my situation:

 

I have a module that contains a $ amount for a list of accounts , I am then mapping those $ amounts to another module that contains line items that I have in a List. 

 

In my screenshot you can see in Line item Mapto contains values of the list as well as Line Item Mapto2 contains values of the same list. However, I need the percent allocation of the Mapto list items to match the % allocation in % Map to 1 and % Map to 2. 

 

Here is a breakdown:

 

Module 1 contains $1000 for account X

Module 2 contains a line item for Y 

Module 3 is mapping X to Y by using a List that contains (Y,Z,A,B,C etc) 

 

I am summing the list values from Module 3 to produce the value in Module 2

 

The issue I am having is that I need a % of Y to be pulled from X while the other % will go to another value in the list such as B or C.

 

How can I accomplish this?