Explanation:
-3|2a - 4| >= -12
3|2a - 4| <= 12 | when we multiply by a
| negative number, then
| the inequality reverses.
|2a - 4| <= 4
that is only the case for
0 <= a <= 4
because
|0 - 4| = 4
|2 - 4| = 2
|4 - 4| = 0
|6 - 4| = 2
|8 - 4| = 4
any value for a < 0 or > 4 leads to expressions > 4.