An individual has a portfolio that consists of

1) a three year zero coupon bond with a maturity value of $5000 and a yield of 5%

2) a four year zero coupon bond with a maturity value of $5000 and a yield of 6% and

3) a perpetuity of dividends from a common stock , where the first dividend is $100 and is paid one year from now, and each dividend is 3% higher than the prior one. The yield is 6%.

What is the duration of this portfolio