The manager of a manufacturing factory needs to decide between two different machines. Machine A will have an initial cost of $40,000, an annual operating cost of $30,000, and a service life of 4 years. Machine B will cost $50,000 to purchase, an annual operating cost of $18,000 with 4-year life. At an interest rate of 10% per year, which should be selected on the basis of a present worth analysis?