4. Imagine that there are two approaches to solving a particular environmental problem. The first approach involves an initial investment of $500M, ongoing costs of $1M each year and, at the end of the 50-year planning horizon, will leave an asset with a residual value of $300M. The second approach involves an initial investment of $300M, ongoing costs of $5M each year and at the end of the 50-year planning horizon, will require $50M to remove the installation and remediate the associated land. Assuming that the projects are otherwise similar with regard to reliability, sustainability and robustness, how do the present value of the costs of each project compare? How does your answer depend on the interest rate you use to discount future time periods and at what interest rate do the two projects have equal costs?