8. The real numbers $x, y$ and $z$ are a solution $(x, y, z)$ of the equation $\left(x^{2}-9\right)^{2}+\left(y^{2}-4\right)^{2}+\left(z^{2}-1\right)^{2}=0$. How many different possible values are there for $x+y+z ?$