I have this problem that I do not understand how to do it.
1-3 | 7-x | < or equal to -11
I got (- infinity, 3] U [ 11,infinity)
1 - 3|7-x| ≤ -11
-3|7-x| ≤ -12
|7-x| ≥ 4
7-x ≥ 4 or -7+x ≥ 4
-x ≥ -3 or x ≥ 11
x ≤ 3 OR x ≥ 11
I think that matches your answer.