An existing machine in a factory has an annual maintenance cost of 40,000 pesos. A new and more efficient machine will require an investment of 90,000 pesos and is estimated to have a salvage value of 30,000 pesos at the end of 8 years. Its annual expenses for maintenance total to 22,000 pesos. If the company expects to earn 12% on its investment, will it be worthwhile to purchase the new machine using the a) present worth method? b) rate of return method