Question

−6 <3n+9 <21. whats the solution

Answer 1

We have

$-6 < 3n+9 < 21$.

From this we have system of inequality

$-6 < 3n+9 \\3n+9 < 21$

We have to simplify both inequalities

$3n+9 > -6 \Longrightarrow n > -5 \\3n+9 < 21 \Longrightarrow n < 4$

So we can conclude that

$n > -5 \wedge n < 4 \Longrightarrow x\in(-5,4)$

Hope this helps.