Please show work in excel

a$.$ What is the duration of a four$-$year Treasury bond with a $9\mathrm{.}5$ percent semiannual coupon selling at par?

b$.$ What is the duration of a three$-$year Treasury bond with a $9\mathrm{.}5$ percent semiannual coupon selling at par?

c$.$ What is the duration of a two$-$year Treasury bond with a $9\mathrm{.}5$ percent semiannual coupon selling at par?