An anticipated purchase of equipment for $520,000, with a useful life of 8 years and no residual value, is expected to yield the following annual net incomes and net cash flows:

Year	Net Income		Net Cash Flow
1	$60,000		$120,000
2	50,000		110,000
3	50,000		110,000
4	40,000		100,000
5	40,000		80,000
6	40,000		80,000
7	40,000		60,000
8	40,000		60,000

What is the cash payback period?

a.4 years

b.6 years

c.5 years

d.3 years