Separate the inequalities by part.
[tex]8<12+c\\12+c<12[/tex]
We'll do 8 < 12+c first then 12+c<12 next.
[tex]8-12<c\\-4<c\\c>-4[/tex]
Then 12+c<12
[tex]12+c<12\\c<12-12\\c<0[/tex]
Then mix c<0 and c>-4 as we'll get [tex]-4<c<0[/tex] #
