12. The parabolas $y=x^{2}-b x$, $y=-x^{2}+b x$ and the line $y=k x$ can divide the plane into at most
$\qquad$ parts.
12. 9 .

Two parabolas are symmetric with respect to the $x$-axis, and the origin is their common point. Also, the line $y=k x$ intersects them at most at 3 points, so it can be known that the plane is divided into at most 9 parts.