given the following cash flows: initial investment at time 0: $400,000 net cash inflows: time 1: $20,000; time 2: $70,000; time 3: $110,000; time 4: $200,000; time 5: $400,000. (please note that time 0 is the start of year 1 and time n is the end of year n - for example time 5 is the end of year 5.) what is the payback period?