Two methods are under consideration for producing the case for a portable hazardous material photoionization monitor. A plastic case will require an initial investment of $75,000 and will have an annual operating cost of $27,000 with no salvage after 2 years. An aluminum case will require an investment of $125,000 and will have annual costs of $12,000. Some of the equipment can be sold for $30,000 after its 3-year life. At an interest rate of 10% per year, which case should be used on the basis of a present worth analysis