#### Answer

$$\begin{bmatrix}
9&1&-3&\vdots&21 \\0&-15&13&\vdots &-8
\end{bmatrix}$$

#### Work Step by Step

In order to write a matrix that would solve this linear equation, we write the coefficients of each variable in their own column. Doing this, we find:
$$\begin{bmatrix}
9&1&-3&\vdots&21 \\0&-15&13&\vdots &-8
\end{bmatrix}$$