As respostas são respectivamente:
[tex]\large\begin{array}{lr}\sf A+B = \left[\begin{array}{ccc}-11&-4\\14&51\\10&5\end{array}\right] \end{array}[/tex]
[tex]\large\begin{array}{lr}\sf A-B = \left[\begin{array}{ccc}5&14\\-10&-39\\-2&11\end{array}\right] \end{array}[/tex]
Para que possamos somar ou subtrair matrizes basta somarmos ou subtrairmos termos que estejam na mesma posição em ambas as matrizes. Veja abaixo a resolução de sua questão.
[tex]\large\begin{array}{lr}\sf A = \left[\begin{array}{ccc}-3&5\\2&6\\4&8\end{array}\right] + B = \left[\begin{array}{ccc}-8&-9\\12&45\\6&-3\end{array}\right]\end{array}[/tex]
[tex]\large\begin{array}{lr}\sf A+B = \left[\begin{array}{ccc}-3+(-8)&5+(-9)\\2+12&6+45\\4+6&8+(-3)\end{array}\right] \end{array}[/tex]
[tex]\large\begin{array}{lr}\boxed{\boxed{\sf A+B = \left[\begin{array}{ccc}-11&-4\\14&51\\10&5\end{array}\right] }}\end{array}[/tex]
[tex]\large\begin{array}{lr}\sf A = \left[\begin{array}{ccc}-3&5\\2&6\\4&8\end{array}\right] - B = \left[\begin{array}{ccc}-8&-9\\12&45\\6&-3\end{array}\right]\end{array}[/tex]
[tex]\large\begin{array}{lr}\sf A-B = \left[\begin{array}{ccc}-3-(-8)&5-(-9)\\2-12&6-45\\4-6&8-(-3)\end{array}\right] \end{array}[/tex]
[tex]\large\begin{array}{lr}\boxed{\boxed{\sf A-B = \left[\begin{array}{ccc}5&14\\-10&-39\\-2&11\end{array}\right]}} \end{array}[/tex]
Veja mais sobre matrizes:
[tex]\square[/tex] brainly.com.br/tarefa/23708979
[tex]\square[/tex] brainly.com.br/tarefa/22649942
[tex]\square[/tex] brainly.com.br/tarefa/6040180
[tex]\square[/tex] brainly.com.br/tarefa/41604378
Espero ter ajudado.
Bons estudos.
