What is the duration of a 4-year bond with an annual coupon rate of 9%? Its value at maturity is $1,000, the current bond price is $1,103.96, and the yield to maturity is 6%. The present values of cash flows from Year 1 through Year 4 are $84.91, $80.10, $75.57,and $863.38.

a. 2.44

b. 3.23

c. 3.56

d. 4.1