A 2,000-pound, counterbalanced, propane forklift can be purchased for $30,000. Due to the intended service use, the forklift's market value drops 20% of its prior year's value in Years 1 and 2 and then declines 15% until Year 10 when it will have a scrap/ market value of $1,000. Maintenance of the forklift is $400 per year during Years 1 and 2 while the warranty is in place. In Year 3 it jumps to $750 and increases by $200 per year thereafter. What is the optimal life of the forklift using i = 10%