Lexington Power Systems is comparing four machines, each of which uses a different technology, to determine which one to purchase. The machines sell for differing prices, have differing operating costs, differing machine lives, and whichever type is chosen will be replaced when worn out. Which one of the following computational methods should Lexington use as the basis for its decision?

a.)		internal rate of return
b.)		operating cash flow
c.)		equivalent annual cost
d.)		depreciation tax shield
e.)		bottom-up operating cash flow