Please help me solve this question and explain

Consider an investment with an initial cost of $20,000 which is expected to last for 5 years. The expected cash flow in years 1 and 2 are $5,000, in years 3 and 4 are $5,500 and in year 5 is $1,000. Compute the payback period in years. 3.18 years 3.82 years 4.00 years 4.55 years