A transportation agency can construct a project that will reduce crash counts & severities, on average. The project has an initial price tag of $$3\mathrm{.}5M$ and a required annual maintenance of $$65,000$ over an expected project life of $15$ years. Current crash costs are estimated to be $51\mathrm{.}9M$ per year in the first year if nothing is done, and will rise by $5\%$ annually. If a $4\%$ discount rate is assumed and only safety benefits are considered, what is the minimum percentage crash reduction needed to make this project worthwhile? $($Assume that the initial costs are spent immediately, and$]$all crash reduction benefits and maintenance costs are realized at the end of each year.$)$ If the discount rate is changed to $10\%,$ what is the new minimum crash reduction rate to ensure an NPV at least $S2M?$ What is the $\frac{B}{C}$ ratio in this case?

Hint: Make a working spreadsheet where changing critical values will update figures quickly.