7 A consulting engineering firm is considering two models of SUV for the company principals. A GM model will have a first cost of $36,000, an operating cost of $4000, and a salvage value of $15,000 after 3 years. A Ford model will have a first cost of $32,000, an operating cost of $3100, and also have a $15,000 resale value, but after 4 years. (a) At an interest rate of 15% per year, which model should the consulting firm buy? Conduct an annual worth analysis. (b) What are the PW values for each vehicle