Jason has purchased 3 bonds (all of them are redeemable at par with face value $1000) to establish the following portfolio: (i) Bond A has semiannual coupon of 6%, a Macaulay duration of 18.71 years, and was purchased for $1,182.56. (ii) Bond B is a 15-year bond with Macaulay duration of 11.34 years and was purchased for $896.20. (iii) Bond C is a zero-coupon bond maturing in 12 years and was purchased for $556.84. Calculate the Macaulay duration (in years) of the portfolio at the time of purchase. (A) 13.82 (B) 14.38 (C) 14.79 (D) 15.00 (E) 15.26