use formulas to calculate

IV. (Example problem: Don't turn in): The crane above is purchased for $36,000. The salvage value after 1 year is $24000 and this continues to drop by $4000 each year The operating and maintenance costs are $10,000 in the first year and continue to increase by $2500 each year. How long should it be kept before replacing? MARR is 15% (Procedure: Find the annual worth assuming it is kept for 1 year, 2 years, 3 years and so on for 7 years. Pick the year where the annual worth is the least) V.Economic life of an investment: (Read Example IV) A machine is purchased for S100,000. Its market value decreases by $20,000 at the end of year 1 and then decreases by $5000 for each additional year. Operational and maintenance costs start at $11000 at the end of year 1 and increase by $2000 each year after that. Determine after how many years the machine should be replaced. MARR-10%. (You must first find the annual cost for each year that the machine is kept)