Ted and Alice Hansel have a son who will begin college 10 years from today. School expenses of $37,000 will need to be paid at the beginning of each of the four years that their son plans to attend college. What is the duration of this liability to the couple if they can borrow and lend at the market interest rate of 9.7 percent? (Do not round intermediate calculations and round your answer to 5 decimal places, e.g., 32.16161.)