A series of payments are as follows: A payment of C1 = 2000 at time t1 = 1. A payment of C2 = 8000 at time t2 = 4.A payment of C3 = 6500 at time t3 = 10. A payment of C4 = = 10750 at time t4 = 13. Using an annual effective rate of interest of i = 6.6%, determine the Macauley duration. Enter your answer to two decimal places