Jiajin Industry Co., Ltd. plans to invest 15,500 yuan to buy a piece of equipment, which is expected to be used for 3 years with a residual value of 500 yuan. Depreciation is based on the straight line method. After the equipment is put into operation, it is expected that the annual increase in sales revenue will be RMB 10,000, RMB 20,000 and RMB 15,000 respectively, and the increase in expenses excluding depreciation will be RMB 4,000, RMB 12,000 and RMB 5,000 respectively. The applicable income tax rate of the company is 25%, and the required minimum rate of return is 10%. At present, the company's after-tax profit is RMB 20,000.

(1) Assuming there is no other change in business operation, the after-tax profit in each of the next three years is predicted.

(2) Calculate the payback period of the investment plan.

(3) Calculate the net present value of the scheme.