Calculate a sum of an accountlist with hfm rules or wdef

Hello, i am looking for a solution to calculate a sum of an accountlist for all children of a parent entity.

I generated an accountlist and now i want to calculate a sum of all the members of this accountlist for some parent entities.

There are 100 parent entities and i need the sum of an accountlist for each of the 100 parent entities.

I don´t have build much rule files or wdef´s, so i hope here is someone who can help me.

Best wishes

Martin