Lizzy: A library cabinet houses five ancient scrolls. The first scroll is 4080 years old. If each scroll is older than the last by half as many years as the last scroll’s age, how old is the fifth scroll?.
Me: Hmmm, let me think. I think this is the detailed solution:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
The second scroll is 4080 + 4080 / 2 = 4000 + 2040 = 6120 years old. The third scroll is 6120 + 6120 / 2 = 6120 + 3060 = 9180 years old. The fourth scroll is 9180 + 9180 / 2 = 9180 + 4590 = 13770 years old. The fifth scroll is 13770 + 13770 / 2 = 13770 + 6885 = 20655 years old. Final answer: 20655.