$$f ( x ) = \left\{ \begin{array} { l l l }
10 - x ^ { 2 } & , & x < 0 \\
a x + b & , & 0 \leq x \leq 3 \\
( 1 - x ) ^ { 2 } & , & x > 3
\end{array} \right.$$
The function is continuous on the set of real numbers.
Accordingly, what is the sum $\mathbf { a } + \mathbf { b }$?
A) 16
B) 15
C) 12
D) 9
E) 8