Application of Derivatives

Let $$f: \rightarrow \mathbb{R} \rightarrow(0, \infty)$$ be strictly increasing function such that \lim _\limits{x \rightarrow \infty} \frac{f(7 x)}{f(x)}=1. Then, the value of \lim _\limits{x \rightarrow \infty}\left[\frac{f(5 x)}{f(x)}-1\right] is equal to