Let f(n)f(n)f(n) be a recursive function defined by: f(n)={n−3if n>20f(f(n+5))if n≤20f(n) = \begin{cases} n - 3 & \text{if } n > 20 \\ f(f(n+5)) & \text{if } n \leq 20 \end{cases}f(n)={n−3f(f(n+5))if n>20if n≤20 Determine the value of f(15)f(15)f(15).
18
17
19
20