Consider the matrices : $A = \left[ \begin{array} { c c } 2 & - 5 \\ 3 & m \end{array} \right] , B = \left[ \begin{array} { l } 20 \\ m \end{array} \right]$ and $X = \left[ \begin{array} { l } x \\ y \end{array} \right]$. Let the set of all $m$, for which the system of equations $A X = B$ has a negative solution (i.e., $x < 0$ and $y < 0$ ), be the interval ( $a , b$ ). Then $8 \int _ { a } ^ { b } | A | d m$ is equal to $\_\_\_\_$