A: Problem 19 is an EUAC (Equivalent Uniform Annual Cost) problem — it's finding the annual cost of an investment, which uses an A/P factor from the engineering economics tables. Problem 18, while also involving an annual value, is a different type of analysis. The word 'annualized' is a red flag: always identify whether you're doing present value, future value, or uniform annual series, and which specific factor (P/F, P/A, A/P, etc.) the problem requires before setting up your equation.

A: I need a little more to work with here — the first step of this problem was drawing the cash flow diagram, so if you were able to do that but got stuck downstream, tell me where it broke down and I can help from there. The more specific your question, the more useful my answer will be.