does anyone know how to solve this? I have tried everything, your help would be appreciated. Thank you

a.	What is the duration of a four-year Treasury bond with a 13 percent semiannual coupon selling at par? (Do not round intermediate calculations. Round your answer to 2 decimal places. (e.g., 32.16))

Duration of the bond

years

b.	What is the duration of a three-year Treasury bond with a 13 percent semiannual coupon selling at par? (Do not round intermediate calculations. Round your answer to 2 decimal places. (e.g., 32.16))

Duration of the bond

years

c.	What is the duration of a two-year Treasury bond with a 13 percent semiannual coupon selling at par? (Do not round intermediate calculations. Round your answer to 2 decimal places. (e.g., 32.16))

Duration of the bond

years