Multiply the inequality by -1 to make the coefficient of the highest power in $9-x^{2}$ positive. Since $-1$ is negative, the inequality direction is changed.
$$-9+x^{2}\leq 0$$
Add $9$ to both sides.
$$x^{2}\leq 9$$
Calculate the square root of $9$ and get $3$. Rewrite $9$ as $3^{2}$.
