A company must pay a liability of $1,000 in 2 years. Zero coupon bonds with terms of 1 year and 4 years are available for investment. The effective rate of interest is 7.5%. How much of each bond should the company buy in order to achieve full immunization?

If you decide to use an excel spreadsheet could you maybe provide a brief explanation of the functions you use (or maybe say how it would relate to a financial calculator such as the BA II Plus)