please explain by steps and dont use excel. thank you

Question 14.02 A portfolio consists of 3 bonds: Bond 1 has a duration of 8, and its price is 100. Bond 2 has a duration of 13, and it pays semiannual coupons at an annual rate of 6%. The price of Bond 2 is 75.50. Bond 3 has a duration of 12, and it matures in 20 years. The price of Bond 3 is 60.41. Calculate the duration of the portfolio. A 10.6 B 11.0 C 11.5 D 12.7 E 12.9 -1AA2