rory company has an old machine with a book value of $75,000 and a remaining five-year useful life. rory is considering purchasing a new machine at a price of $90,000. rory can sell its old machine now for $60,000. the old machine has variable manufacturing costs of $33,000 per year. the new machine will reduce variable manufacturing costs by $13,000 per year over its five-year useful life. (a) prepare a keep or replace analysis of income effects for the machines. (b) should the old machine be replaced?