13. In the Cartesian coordinate system $x O y$, point $P(a, b)$, after a certain transformation, gets the corresponding point $P^{\prime}(3 a+ 2,3 b-1)$. Given that $A, B, C$ are three non-collinear points, and after this transformation, their corresponding points are $A^{\prime}, B^{\prime}, C^{\prime}$, respectively. Then the area of $\triangle A^{\prime} B^{\prime} C^{\prime}$ is $\qquad$ times the area of $\triangle A B C$.
$9$