Enterprise D invests 15,500 yuan to purchase a piece of equipment. The estimated residual value of the equipment is 500 yuan and can be used for 3 years. The depreciation is calculated by the straight-line method. After the equipment is put into production, the annual increase in sales revenue is 10,000 yuan, 20,000 yuan, and 15,000 yuan, and the increase in expenses other than depreciation is 4,000 yuan, 12,000 yuan, and 5,000 yuan, respectively. The applicable income tax rate for enterprises is 25%, the required minimum return on investment is 10%, and the current annual after-tax profit is 20,000 yuan. Requirements: (1) Assuming that there are no other changes in the operation of the export enterprise, forecast the after-tax profit for each of the next three years.

(2) Calculate the net present value of the investment plan