Function
$$f ( x ) = \left\{ \begin{array} { c c }
\frac { x ^ { 2 } + x - 12 } { x - 3 } & ( x \neq 3 ) \\
a & ( x = 3 )
\end{array} \right.$$
When this function is continuous for all real numbers $x$, what is the value of $a$? [2 points]\\
(1) 10\\
(2) 9\\
(3) 8\\
(4) 7\\
(5) 6