an electric switch manufacturing company is trying to decide between three different assembly methods. method a has an estimated first cost of $44,000, an annual operating cost (aoc) of $5,000, and a service life of 2 years. method b will cost $84,000 to buy and will have an aoc of $10,000 over its 4-year service life. method c costs $143,000 initially with an aoc of $5,000 over its 8-year life. methods a and b will have no salvage value, but method c will have equipment worth 10% of its first cost.