Find Constants a and B Such That the Function $$f ( x ) = \left\{ \begin{array} { l l } 18 , & x \leq - 3 \\ax + b , & - 3 < x < 9 \\- 18 , & x \geq 9\end{array} \right.$$

Multiple Choice

Find constants a and b such that the function $$f ( x ) = \left\{ \begin{array} { l l } 18 , & x \leq - 3 \\ax + b , & - 3 < x < 9 \\- 18 , & x \geq 9\end{array} \right.$$ is continuous on the entire real line.

A) a = 3 , b = 0
B) a = 3 , b = 9
C) a = 3 , b = -9
D) a = -3 , b = -9
E) a = -3 , b = 9