Help please!

9. An investor purchases 5 zero-coupon bonds, with terms of 1, 2, 3, 4, and 5 years. Each bond has a maturity value of 1,000, and is priced based on the following yield curve: Term (yrs.) Spot rate 2.4% 1 3.0% 3.4% 4 3.7% 5 3.9% What is the modified duration of the investor's portfolio? 2 3