\(3-4n⋮n+1\Rightarrow7-4-4n⋮n+1\)
\(\Rightarrow7-4\left(n+1\right)⋮n+1\)
\(\Rightarrow7⋮n+1\)
\(\Rightarrow n+1=Ư\left(7\right)=\left\{-7;-1;1;7\right\}\)
\(\Rightarrow n=\left\{-8;-2;0;6\right\}\)
Do n là số tự nhiên \(\Rightarrow n=\left\{0;6\right\}\)