We issue 2,000 invoices each month globally. Assume average time to complete is 20 minutes. We issue 100 credit memos each month globally. Assume average time to complete is 30 minutes.

How many invoicing staff, at a 40 hour week, will it take to keep up with this volume?

Please state your answer as algebra. If the number of invoices increase at a rate of 5% per month, when will you add an additional person?