You can't sumamrize it. You would have to use shared variable formulas.
That said conside this:
I assume you have a (small) risk of missing a revenue charge that is the same on a subsequent row but is not actually a duplicate and this formula excluding it.
I also assume you are using this becasue you have duplicate rows in teh report because of joins.
I also would hazard a guess you have a unique PK field from your charge table.
If these assumptions are corerct a better way to handle this is to use teh PK form charges and eitehr a Running Total (RTs) or shared variable formulas that use the PK as a the key to include or excldeu a row.
I prefer RTs
In this case you would create a runnnig total
name=group_charges (or whatever)
field to summarize =revenue.charge
type=sum
evaluate= on change of field charges.PK_field
reset= on group (select the group you want to display it on)
place in group footer as RTs do not work in Headers