d is neither a or b

A compressor train for an offshore installation is due for replacement Systems from two different vendors are being considered with the estimated cost data shown below. The alternatives shown are to be compared on the basis of their annual worth values. At an interest rate of 10% per year, the values of n that you should use in the (A/P, i, n) factors to make a correct comparison by the annual worth method are: First cost, $ Annual operating cost, $ per year Salvage value, $ Life, years Alternative A 50,000 10,000 13,000 3 Alternative B 90,000 4,000 15,000 6 a. n = 3 years for A and n=3 years for B b. n = 3 years for A and n=6 years for B Either (a) or (b)