$\begin{array}{ll}A=\left[\begin{array}{ll}9 & 9 \\ 8 & 4\end{array}\right] & B=\left[\begin{array}{ll}3 & 1 \\ 1 & 9\end{array}\right] \\ C=\left[\begin{array}{ll}3 & 7 \\ 7 & 0 \\ 0 & 1\end{array}\right] & D=\left[\begin{array}{rr}20 & 30 \\ 30 & 20 \\ 10 & 0\end{array}\right] \\ 2 X+A=B\end{array}$
Answer
\(\boxed{X = \left[\begin{array}{rr}-3 & -4 \\ -3.5 & 2.5\end{array}\right]}\)
Step 1 ：Subtract matrix A from matrix B: $B - A = \left[\begin{array}{rr}3-9 & 1-9 \\ 1-8 & 9-4\end{array}\right] = \left[\begin{array}{rr}-6 & -8 \\ -7 & 5\end{array}\right]$
Step 2 ：Divide the resulting matrix by 2: $X = \frac{1}{2} \left[\begin{array}{rr}-6 & -8 \\ -7 & 5\end{array}\right] = \left[\begin{array}{rr}-3 & -4 \\ -3.5 & 2.5\end{array}\right]$
Step 3 ：\(\boxed{X = \left[\begin{array}{rr}-3 & -4 \\ -3.5 & 2.5\end{array}\right]}\)
