Today is 1 July, 2019. Andrew has a portfolio which consists of two different types of financial instruments (henceforth referred to as instrument A and instrument B). Andrew purchased all instruments on 1 July 2014 to create this portfolio, which is composed of 36 units of instrument A and 35 units of instrument B.

• Instrument A is a zero-coupon bond with a face value of $100. This bond matures at par. Its maturity date is 1 January 2029.
• Instrument B is a Treasury bond with a coupon rate of j₂=2.94% p.a. and a face value of $100. This bond matures at par. Its maturity date is 1 January 2022.

Calculate the current duration of Andrew's portfolio using a yield to maturity of j₂=3.81% p.a. Express your answer in terms of years and round your answer to two decimal places.

Answer options:

a. 7.04 years

b. 5.37 years

c. 6.57 years

d. 5.42 years