Fuel

Find the average miles per gallon the truck uses, and divide by milage each person drives.

 

How 'bout pay your friend by the mile or by the trip and you and your dad continue to share the P&L.

 

Gees ... just take the entire amount used in a week and ...

Either divide it up by the days the truck was used and split the costs equally

Or

divide it up by the days run and then for each day divide it up by the number of people who used it for that day, then add that number to their total for the week.

I know this sounds complex but remember this is a business and costs are not calculated to the penny because it is impossible to be accurate like that, so shared costs are really the best way to figure this.