Suppose \(f : \mathbb{R} \rightarrow (0, \infty)\) be a differentiable function such that \(5 f(x+y) = f(x)\cdot f(y), \; \forall \, x, y \in \mathbb{R}\). If \(f(3) = 320\), then \(\displaystyle \sum_{n=0}^{5} f(n)\) is equal to:
6825
6525
6575
6875