For a triangle $ABC$, $\overrightarrow{AB}=-2\hat i+\hat j+3\hat k$ $\overrightarrow{CB}=\alpha\hat i+\beta\hat j+\gamma\hat k$ $\overrightarrow{CA}=4\hat i+3\hat j+\delta\hat k$ If $\delta>0$ and the area of the triangle $ABC$ is $5\sqrt{6}$, then $\overrightarrow{CB}\cdot\overrightarrow{CA}$ is equal to: