Chapter 9 - Systems and Matrices - 9.7 Properties of Matrices - 9.7 Exercises - Page 930: 42

$\left[\begin{array}{ll} 18 & -6\\ -12 & 0 \end{array}\right]$

We are given that $B=\left[\begin{array}{ll} -6 & 2\\ 4 & 0\end{array}\right]$ Now, $-3B=-3 \left[\begin{array}{ll} -6 & 2\\ 4 & 0\end{array}\right]=\left[\begin{array}{ll} -6 (-3)& 2(-3)\\ 4 (-3)& 0(-3)\end{array}\right]\\=\left[\begin{array}{ll} 18 & -6\\ -12 & 0 \end{array}\right]$