Cost Per Ticket

I am trying to create a calculation metric to determine cost per ticket by month for this year. I tried using tickets solved - month / full resolution time business hours. Unfortunately, only the later field was available in minutes. The outcome did not seem right when I calculated the number manually on my own. What would be the exact formula to calculate the cost per ticket over this time period? The fields and/or functions may not be correct which is throwing things off. I have made several different efforts with the same wrong result. Any help would be greatly appreciated it. Thank you!