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 $4.1 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 22 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 $ .