Please explain how they got $1.12 per hour?

Total interest paid on a loan can be determined by an index found in a credible finance book or online calculator. For the purpose of cost analysis, interest is calculated on a per hour basis. A general formula to calculate interest paid per hour:

Assuming the total interest paid on a tractor loan of $80,000.00 paid at 10% over five years is $48,840.80: Interest paid on a tractor is $1.12 per hour.