Function Problem If $f(x)$ is a function satisfying $ \displaystyle f(x+y) = f(x) \cdot f(y)  \text { for all } x,y \in \mathbb{N} \text{ such that } f(1) = 3 \text { and } $ $ \sum_{x=1}^{n} f(x) = 120 $, then find the value of $n$.
How to approach this one?

Hint: Knowing the value of $f(1)$, you can get the value of $f(2)=f(1+1)$ from the defining equation. Knowing these two, you can get value of $f(3)=f(1+2)$ and so on.
