Represent linear systems with matrix equations

Represent systems of two linear equations with matrix equations by determining A and b in the matrix equation A*x=b.

Problem

The following system of equations is represented by the matrix equation A[xyz]=b\text{A}\left[\begin{array} {ccc} x \\ y \\ z \end{array} \right]=\vec{b}.
10x5y=2015x+20y=812x+5y20z=30\begin{aligned}10x-5y&=20 \\15x+20y&=-8 \\12x+5y-20z&=30\end{aligned}
b, with, vector, on top, equals
Represent each row and column in the order in which the variables and equations appear.