Answer :

[tex]n+5(n-1)=7 \\\\ n+5n-5=7 \\\\ 6n-5=7 \\\\ 6n=7+5 \\\\ 6n= 12 \\\\ \boxed{n=\frac{12}{6}=2}[/tex]
n+5(n-1)=7
n+5=7
  -5=-5
n=2

n-1=7
  +1=+1
n=8