An anticipated purchase of equipment for $490,000 with a useful life of 8 years and no residual value is expected to yield the following annual incomes and net cash flows:

Year	Income	Net Cash Flow
1	$60,000	$110,000
2	50,000	100,000
3	50,000	100,000
4	40,000	90,000
5	40,000	90,000
6	40,000	90,000
7	40,000	90,000
8	40,000	90,000

The cash payback period for the equipment is

a. 3 years

b. 4 years

c. 6 years

d. 5 years