TeX source:
\begin{array}{rclcl rclcl}\text{1. Fall} & & & & & \text{2. Fall} \cr20 &=& 2z+8 &\vert& -8 & 20 &=& -2z-8 &\vert& +8 \cr 12 &=& 2z &\vert& : 2 & 28 &=& -2z &\vert& : \left(-2\right) \cr 6 &=& z_2 & & & -14 &=& z_3 & & \end{array}