An engineer has received two bids for an elevator to

be installed in a new building. Given a 10% interest
rate, which bid should be accepted?
Alternatives Westinghome Itis
Installed cost $45,000 $54,000
Annual cost 2700 2850
Salvage value 3000 4500
Life, in years 10 15

Can you help me with what present worth formula to use??