Please urgent solve it accurately and completely.

3) An investment project has an initial cost of $680 and cash flows $150, $330, $280, and $105 for Years 1 to 4, respectively. The discount rate is 9 percent. What is the discounted payback period? Show your formulalcalculation/explanation! 4- You can buy a piece of land today for $15,000, including the cost of some minor repairs. You expect to be able to resell it in one year for $16,000. At a discount rate of 8 percent, what is the expected net present value of this purchase opportunity? Would you buy it? Why? Show your formula/calculation