Find the following matrices where $A=\left[\begin{array}{ll}9 & 2 \\ 6 & 6\end{array}\right]$ and $B=\left[\begin{array}{ll}1 & 8 \\ 1 & 3\end{array}\right]$. a. $A+B$ b. $A-B$ c. $-5 \mathrm{~A}$ d. $3 \mathrm{~A}+4 \mathrm{~B}$ a. Select the correct choice below and, if necessary, fill in the answer box to complete your choice. $A+B=\left[\begin{array}{rr}10 & 10 \\ 7 & 9\end{array}\right]$ (Simplify your answer.) B. This matrix operation is not possible. b. Select the correct choice below and, if necessary, fill in the answer box to complete your choice. A. $A-B=\quad$ (Simplify your answer.) B. This matrix operation is not possible. What is ABC and D?

Step 1 ：Given matrices $A=\left[\begin{array}{ll}9 & 2 \\ 6 & 6\end{array}\right]$ and $B=\left[\begin{array}{ll}1 & 8 \\ 1 & 3\end{array}\right]$.

Step 2 ：For part a, we need to add matrices A and B. Matrix addition is performed element-wise, meaning that the corresponding elements in each matrix are added. So, $A+B=\left[\begin{array}{rr}10 & 10 \\ 7 & 9\end{array}\right]$.

Step 3 ：For part b, we need to subtract matrix B from matrix A. Matrix subtraction is also performed element-wise. So, $A-B=\left[\begin{array}{rr}8 & -6 \\ 5 & 3\end{array}\right]$.

Step 4 ：For part c, we need to multiply matrix A by -5. This is a scalar multiplication which involves multiplying every element in the matrix by the scalar. So, $-5A=\left[\begin{array}{rr}-45 & -10 \\ -30 & -30\end{array}\right]$.

Step 5 ：For part d, we need to multiply matrix A by 3, multiply matrix B by 4, and then add the two resulting matrices together. So, $3A+4B=\left[\begin{array}{rr}31 & 38 \\ 22 & 30\end{array}\right]$.

Step 6 ：Final Answer: \(\boxed{A+B=\left[\begin{array}{rr}10 & 10 \\ 7 & 9\end{array}\right]}\), \(\boxed{A-B=\left[\begin{array}{rr}8 & -6 \\ 5 & 3\end{array}\right]}\), \(\boxed{-5A=\left[\begin{array}{rr}-45 & -10 \\ -30 & -30\end{array}\right]}\), and \(\boxed{3A+4B=\left[\begin{array}{rr}31 & 38 \\ 22 & 30\end{array}\right]}\).