Answer:
the formula to calculate modified duration of bonds:
modified duration = [1 - (1 + y)⁻ⁿ] / y
since this bond pays semiannual interest,
modified duration = [1 - (1 + 6.5%)⁻⁶] / 6.5%
modified duration = (1 - 1.065⁻⁶) / 6.5% = 4.841 semiannual periods
modified duration in years = 4.841 / 2 = 2.4205 years
if you want to determine the Macaulay duration = modified duration x (1 + yield) = 2.4205 years x 1.065 = 2.5778 years