The City of San Antonio is considering various options for providing water in its $50-$year plan, including desalting. One brackish aquifer is expected to yield desalted water that will generate revenue of $$4\mathrm{.}1$ million per year for the first $4$ years, after which less production will decrease revenue by $10\%$ per year each year. If the aquifer will be totally depleted in $25$ years, what is the present worth of the desalting option revenue at an interest rate of $7\%$ per year?

The present worth of the desalting option revenue at an interest rate of $7\%$ per year is determined to be $$4210933.$