Answer:
f(w) = $100 + $15*w
Explanation:
The first $100 she deposited remain always the same, they don't change depending on the weeks. What increases along the weeks are the $15.
In the first week she will deposit $15, so she will have $100 + $15 = $115.
On the second week she will deposit $15 more, so she will have $115 + $15 = $130. Another way of writing this is $100 + $15 + $15 = $100 + $15*2.
On the third week she will have $100 + $15 + $15 + $15 = $100 + $15*3.
Therefore, after w weeks, she will have $100 + $15*w.
The function we are looking for is f(w) = $100 + $15*w