Let $T$ be the linear transformation defined by

$T(x_1,x_2,x_3) = (x_1 - 5 x_2,\, 8 x_1 - 9 x_2 - 3 x_3,\, x_1 - 6 x_2+ 2 x_3,\, 4 x_1+ 7 x_3)$.

Its associated matrix $A$ is an $n\times m$ matrix,

where $n=\,$ , and $m=\,$ .