I have a spreadsheet that totals complaints per contractor each day.
The contractors get charged a fee per complaint. I want this fee to be
progressive, meaning, for example they would get charged $3.00 for the
first complaint, $4.00 for the second, $5.00 for the third, etc. The
number of complaints on any given day would usually be in the range from
1 to 10 per day. So if they had 5 complaints it would be 1*3+1*4+1+1*5+
etc up to 5 or a total charge of $25.00. Obviously another way to do
this would be to simply add 3+4+5+6+7. But I do want to be able to
alter the amount I charge them per complaint so it won't always be this
progression. For example, they may get their first complaint for free
and then the charges start, or perhaps the first 3 for free and then the
charges start...

Can you help me with a formula