Simple...
so you have...
[tex] \frac{4}{5} n- \frac{3}{5} = \frac{1}{5} n[/tex]
You want to isolate the variable,n,....
so subtract....
[tex] \frac{4}{5} n- \frac{3}{5} = \frac{1}{5} n[/tex]
[tex]- \frac{4}{5}n [/tex] [tex] -\frac{4}{5} n[/tex]
Leaving you with.....
[tex] -\frac{3}{5} = -\frac{3}{5} n[/tex]
Now, divide....
[tex] \frac{- \frac{3}{5} }{ -\frac{3}{5} } = \frac{- \frac{3}{5}n }{ -\frac{3}{5} } [/tex]
Making n=1
Thus, your answer.
