Answer
$f(x)=-\dfrac{1}{6}(x+3)(x-1)(x-4)$
Work Step by Step
Here, we have $f(x)=a (x-(-3))(x-1)(x-4)$
or, $f(x)=a (x+3)(x-1)(x-4)$
When $x=3$, then we have $2=a(3+3)(3-1)(3-4)$
or, $-12a=2$
This gives: $a=-\dfrac{1}{6}$
Thus, we have $f(x)=-\dfrac{1}{6}(x+3)(x-1)(x-4)$