Answer
The function is neither linear nor exponential.
Work Step by Step
The data is not linear, since $\Delta f(x) / \Delta x$ is not constant, nor can it be exponential, because between $x=15$ and $x=12$, we see that $f(x)$ doubles while $\Delta x=3$. When $x=15$ and $x=16$, we see that $f(x)$ doubles while $\Delta x=1$, so the percentage increase is not constant. Thus, the function is neither linear nor exponential.
