A small enginering office in Ontario is considering buying a 3-D printing machine. The office is choosing between two 3-D printing machines that use Fused Deposition Modeling (FDM) technology. The office has a MARR (Minimum Acceptable Rate of Return) of 7%. The salvage value for both machines at the end of their service lives is expected to be $400. Use the information in the table below to answer the following questions.

	Machine A	Machine B
Price	$6,400	$4,400
Running cost per year	$1,200	$1,400
Maintenance cost	$600 for the first year, increasing by $100/year thereafter	$400 for the first year, increasing by $140/year thereafter
Life	6 year	4 years

a) State the necessary assumption to compare mutually exclusive alternatives of different lives.

b) Which alternative is more economic based on Annual Worth comparison?

c) Which alternative is more economic based on Present Worth comparison?

d) For a four-year study period, what salvage value for machine A would make it the preffered choice?

e) Do both methods (Present Worth and Annual Worth) always yield to the same decision?