To prove given $ r \cdot f_1+f_2\cdot (s+1)$ one who knows $f_2$ cannot find out what $f_1$ is

Question

We define the polynomials $r,f_1,f_2,s\in R[x]$. Where $r$ is a random degree 1 polynomial and $s$ is a random polynomial such that: $\deg(s)=\deg(f_1)=\deg(f_2)$. Let $R$ be $\mathbb {Z}_q$ where $q$ is a large prime number

My question: how to To prove "Given $r\cdot f_1+f_2 \cdot (s+1)$ one who knows only $f_2$ cannot learn anything about $f_1$."?

Thanks.