Answer:
 1.8356 years
Explanation:
The computation of the purchase of maturity bond is shown below:
Years (A)    Payment    PVF at 9%    PV         Weight (B)  Duration (A × B)
1 Â Â Â Â Â Â Â Â Â $8,000,000 Â Â Â Â 0.9174 Â $7,339,449.54 Â Â 0.7215 Â Â 0.7215
4 Â Â Â Â Â Â Â Â $4,000,000 Â Â Â Â 0.7084 Â $2,833,700.84 Â Â 0.2785 Â Â 1.1142
                               $101,731,503.39  1       1.8356