Engineering Economy 7th Edition by Leland Blank ,Anthony Tarquin

Exercise 40

Brad and Sheryl are the same age. Brad determined that most of their investments make an average of 6% per year. With this as the interest rate, the analysis for the four alternatives is possible. Sheryl and Brad plan to answer the following questions, but don't have time this week. Can you please help them (Do the analysis for one person at a time, not the couple, and stop at the age of 85.)
Economically, what is the best combination of plans for Brad and Sheryl, assuming they both live to be 85 years old