A project will cost $50,000 initially. The benefits at the end of the first year are estimated to be $10,000, increasing at a rate of 10% in each of the following years for 8 years. Using a 10% interest rate, the simple payback period is closest to

a) 1.45

b) 2.12

c) 4.25

d) 4.32

e) 3.70

I know the answer is 4.25, but do not know how to get it.