Question

How do you solve
-3<7c +4<18

Answer 1

`-3 < 7c+4 < 18\implies -7 < 7c < 14\implies \cfrac{-7}{7} < c < \cfrac{14}{7}\implies -1 < c < 2 \\\\\\ ~\hfill \begin{cases} c > -1\\\\ c < 2 \end{cases}~\hfill`

is just a triplet, so you can always just see it as two inequalities, as -3 < 7c + 4 and 7c + 4 < 18, and do them independently, but the result will be the same as done simultaneously.