please answer part a

A new machine is being considered as a replacement for a current machine machine was purchased 12 years ago for $45,000, with an estimated life of 20 years with no salvage. Current market value is thought to be $40,000. Last year, this machine produced revenues of $25,425 while incurring cash operating expenses of $7.429, Inflation has been averaging 7% per year and revenues have been fully responsive while maintenance costs have been increasing 23% per year. Market value of the machine is expected to decline by 14% per year The current The new machine will cost $53,500. Life and salvage are unknown. Revenues will be the same as the current machine, and cash operating costs will be $5,000 the first year and increase by 11% per year. For the old machine, DDB switching to SYD after 2 years has been used. 7 Year MACRS will be used for the new machine. The tax rate is 50% on ordinary income, and 25% on capital gains. a. Use IRR techniques to find how long the current machine should be kept. b. Caleulate the rate of return for the new machine, and on the incremental (B-A) investment. Assume the new machine will last for the length of time calculated in part a, and that salvage for the current machine at that time will be equal to its market value