What is the payback if the investment is $22,000 and the after tax benefits are: Years 1 & 2 = $2,500 per year Years 3 & 4 = $3,500 per year Years 5 & 6 =$4,000 per year Years 7 & 8 = $4,500 per year Year 9 = $3,000 Year 10 = $1,500