A bond has a remaining maturity of 6 years, a face value of $1000 and irregular principal and coupon payments (see table below). Principal ($) Y (years) 0.5 1.5 3.5 6.0 Coupon ($) 20 60 90 0 250 250 250 250 Assuming the bond is priced at a yield to maturity of 5.5%, what is the modified duration of the bond