Answer: $-3$


Let the number be $y$.

Then $y^3 = 9y\\
y^2\times y = 9\times y$, so either $y=0$ or $y^2 = 9$, giving $y = 3$ or $y = -3$.

$y^2$ is $12$ more than $y$
$y=0\Rightarrow y^2=0$
$y=3$ or $y=-3$ means $y^2=9$ which is $12$ more than $-3$