Answer:
![\left[\begin{array}{ccc}-25&(75)/(2)&-(25)/(2)\end{array}\right]](https://img.qammunity.org/2021/formulas/mathematics/middle-school/5dhtuafba33t1lzmrxsexmoy7g0kmcasfv.png)
Explanation:
In the first equality
![5* \left[\begin{array}{cc}-1&2\\4&8\end{array}\right] =(2)/(5)m* \left[\begin{array}{cc}-1&2\\4&8\end{array}\right],](https://img.qammunity.org/2021/formulas/mathematics/middle-school/mm5bgjre1cepub0fqr5er6c4jfh3py5jif.png)
the matrices in both parts are the saem. The equality will be true if the same matrices are multiplied by the same numbers, so

For the second equality
![(H+[1\ 4\ -2])+[3\ 2\ -6]=[-2\ 3\ -1]+([1\ 4\ -2]+[3\ 2\ -6]),](https://img.qammunity.org/2021/formulas/mathematics/middle-school/46cw5w8mllt195wct5orsjsbyk436d76mi.png)
if
, then this equality represents the assotiative property of matrix addition.
Hence,
![m* H=(25)/(2)* [-2\ 3\ -1]=\left[\begin{array}{ccc}-25&(75)/(2)&-(25)/(2)\end{array}\right]](https://img.qammunity.org/2021/formulas/mathematics/middle-school/r4vmhpat13ars865giykkrib0mrcdft3ua.png)