In desalting groundwater that contains a significant amount of sulfates, the concentrate that is generated during the desalting process can sometimes be tough on equipment, so the equipment’s useful life is uncertain. For a treatment train that has an initial cost of $90,000 and an estimated operating cost (OC) between $15,000 and $20,000 per month, use a spreadsheet to determine how many months the equipment must last to recover the investment at i = 0.5% per month at each OC value? Assume the income from the sale of calcium sulfate is $22,000 per month. Solve using increments of $1000 OC per month.