Add totals in different inline add records

Existing: 1.An inline add of a details table 2. Relevant fieldnames of the details table are a) TotalSuppliers b ) Select c) SupplierAmount
Would like to achieve:

1. For each new inline add record of the details table and
   
2. Where Select = "yes"
   
3. Add the value of TotalSuppliers of that inline add to a field SupplierAmount
   eg
   
   Record--------- TotalSuppliers----------Select---------SupplierAmount
   
   inline add one:--------10------------------yes--------------10
   
   inline add two:--------20------------------no---------------10
   
   inline add three:------30------------------yes--------------40
   NB. The SupplierAmount field value is eventually just forwarded to another tables field, so if it is easier to set this up as a variable or something else it does not need to be setup as a field in the details table.
   I have previously used https://xlinesoft.com/phprunner/docs/how_to_calculate_values_on_the_fly.htm but it seems to refer to calculations in the same inline record rather than calculations across different inline records.
   Any ideas how this can be achieved in an inline add situation?