Answer:
, where w is the number of weeks (natural number) .
Explanation:
Given: Ashley has 100 books that she wants to give away at the rate of n books per week.
Let 'w' be the number of weeks .
Then after first week w=1,
The number of books Ashley has after first week =

[Since she wants to give away at the rate of n books per week.]
Then after second week w=2,
The number of books Ashley has after second week =

Then after third week w=3,
The number of books Ashley has after third week =

Similarly for w weeks, the number of books Ashley has after w weeks =

Hence, the recursive function that gives the number of books Ashley has at any time is
, where w is the number of weeks.