If a $4 \times 4$ matrix $A$ with rows $\vec{v}_1$, $\vec{v}_2$, $\vec{v}_3$, and $\vec{v}_4$ has determinant $\det A = -6$,

then $\ \det$

$\left.\vphantom{\begin{array}{c}\!\strut\\\!\strut\\\!\strut\\\!\strut\\\!\strut\\\end{array}}\right[$ $6 \vec{v}_1+3 \vec{v}_3$ $\left.\vphantom{\begin{array}{c}\!\strut\\\!\strut\\\!\strut\\\!\strut\\\!\strut\\\end{array}}\right]$ $\vec{v}_2$ $8 \vec{v}_1+9 \vec{v}_3$ $\vec{v}_4$

$= \ $

.