A company buys a machine for $500. For the next four years it has annual maintenance expenses of $25. The benefits though are $50 annually. Salvage value at the end of four years is $100. Interest rates are 6%. Draw a complete cash flow diagram with all the informaton. find the present worth 2. Write the equation to find present worth, if the analysis period is infinite. 3. When comparing options with different useful lives, what do you need to find in order to compare them equally?