Answer
A magic square with those numbers could look like:
-12 8 4
16 0 -16
-4 -8 12
Work Step by Step
$(-12) + 8 + 4 = 0$
$16 + 0 + (-16) = 0$
$(-4) + (-8) + 12 = 0$
$(-12) + 16 + (-4) = 0$
$8 + 0 + (-8) = 0 $
$4 + (-16) + 12 = 0$
$(-12) + 0 + 12 = 0$