A. No. The 80% rule of thumb says that retirees need to replace 80% of their income in retirement from various sources to maintain the same standard living they had while working. Unfortunately such simplistic rule doesn't exist and the 80% over-estimates the need for income, for the following reason.
When you start retirement, you no longer contribute to social security, medicare, and your retirement account, that means your replacement rate should be no more than 77% of your final year's salary.
If you subtract other expenses, such as commuting and lower Federal income tax bill, the replacement rate will fall lower.
For more affluent families, they typically don't even spend half of their gross income, which means the 80% rule definitely doesn't apply.
What's the best way to figure out how much income you will need in retirement?
If you are not in retirement yet, it's time to figure out how much exactly you might need in retirement, then plan your retirement income needs based on that.