I will purchase five bonds to form a portfolio. The options for bonds are as follows: Bond A has semiannual coupons at 9.5%, a duration of 10 years, and costs $980. Bond B is a 15-year bond with 6.25% coupons, payable every other year, a duration of 16.5 years, and purchase price of $1715. Bond C has no coupons, but is redeemable in 8 years for its purchase price, $600. Calculate the duration of my portfolio given that I bought 2 of bond A, 1 of bond B, and 2 of bond C