Formula for "Net Amount " in a business process

Hi,



I need help to write the formula for "  Net Amount " in a business process.

The business process is as below screenshot.

When I am trying to use Selection result in Formula popup  I am getting the following error: "Process element "Selection result" not found. "  

 

I need to apply a filter in Commission Rules Selection based on that "Net Amount will be calculated. 

The criteria are as below. "Using the [Distribution_Channel] in the policy register object, query the Commission Rules for that [Distribution_Channel] and cycle through each commission rule. Each rule represents a single Bill. Use the [Commission_Rules.Rate] and [Commission_Rules.Rate_Type] as an input in the formula.

IF [Commission_Rules.Rate_Type] = Percentage

Net Amount = [Base_Premium] x [Commission_Rules.Rate] ELSE

IF [Commission_Rules.Rate_Type] = Flat

Net Amount = [Commission_Rules.Rate] "



Thanks in advance.