The initial capital of a project is 25,000 units of money, 40% of which is to be borrowed and 1/n of the principal of the loan is returned to the bank each year. The bank also receives 10% interest as interest based on the remaining debt at the beginning of each year.

The salvage value of the project after its 5-year useful life is 5,000 units. The depreciation method is DDB (change the method to SL if necessary). Annual gross income is 6,000 units and annual operating cost is 2,000 units. The tax rate for taxable income of less than 1000 currency is 30%. The tax rate for taxable income in excess of 1000 to 2000 currency is 40%. The tax rate for taxable income in excess of 2000 is 50%.

If the annual MARR is 12%, find the NPW before and after the tax deduction and analyze it economically.