Chapter R - Algebra Reference - R.5 Inequalities - R.5 Exercises - Page R-21: 7

$-7\leq x\leq-3$

This is a closed interval. The brackets at either side indicate that both endpoints are included in the interval. So if x is a number in this interval, it will be between $-7$ and $-3$ , with the possibility of being one of the endpoints. We can write this as $-7\leq x\leq-3$