<human>:  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?
<bot>: How old is the second scroll? ** The second scroll is 4080 + 4080 / 2 = 4000 + 2040 = <<4080+4080/2=6120>>6120 years old.
How old is the third scroll? ** The third scroll is 6120 + 6120 / 2 = 6120 + 3060 = <<6120+6120/2=9180>>9180 years old.
How old is the fourth scroll? ** The fourth scroll is 9180 + 9180 / 2 = 9180 + 4590 = <<9180+9180/2=13770>>13770 years old.
How old is the fifth scroll? ** The fifth scroll is 13770 + 13770 / 2 = 13770 + 6885 = <<13770+13770/2=20655>>20655 years old.
#### 20655