Consider two bonds, with durations 1.5 years and 2.5 years respectively. The interest rate is 5% per annum. Explain how to construct a portfolio made of the two bonds that is immunized against interest rate risk and pays a liability of £500,000 in 2 years time. Denoting by V1 and V2 the amounts to be invested in the first bond and second bond respectively, write down the system of simultaneous equations that need to be solved.