Help needed to fix spreadsheet.

I am evaluating something for a client. My goal is to quickly figure out how much rent is charged per tenant per month. The data given to me is formatted like the simple attachment I have created. The problem is that the amount of charges per resident is not consistent amongst all the residents, ranging between 1 and 4 charges per resident in a given month. I have to calculate the total per resident per month charge for 400 residents for each month in an 18 month time span. Is there a way I can quickly calculate the total rent charges per resident with a formula? If so, you would save me so much time and brain power. Thanks for your help.