Let $A(1,1), B(-4,3), C(-2,-5)$ be vertices of a triangle $A B C, P$ be a point on side $B C$, and $\Delta_{1}$ and $\Delta_{2}$ be the areas of triangles $A P B$ and $A B C$, respectively. If $\Delta_{1}: \Delta_{2}=4: 7$, then the area enclosed by the lines $A P, A C$ and the $x$-axis is :