$5.$ Payback Period. Happy Company is planning to spend P$840,000$ for a new machine which it will depreciate in the straight$-$line basis over ten years with no salvage value. The related cash flow from operations, net of income taxes, is expected to be P$100,000$ a year for each of the first six years and P$120,000$ for each of the next four years. What is the payback period?