4x+8=20

(1)  4x+8=20

(2)  -4x+2y=-30

$\begin{array}{lrcl} (1) & 4x+8 &=& 20 \qquad | \qquad -8 \\ & 4x &=& 20 -8 \\ & 4x &=& 12 \qquad | \qquad :4 \\ &\mathbf{x} & \mathbf{=} & \mathbf{3} \end{array}$

$\begin{array}{lrcl} (2) & -4x+2y &=& -30 \qquad | \qquad x = 3 \\ & -4\cdot 3 + 2y &=& -30 \\ & -12 + 2y &=& -30 \qquad | \qquad +12 \\ & 2y &=& -30 + 12 \\ & 2y &=& -18 \qquad | \qquad :2 \\ &\mathbf{y} & \mathbf{=} & \mathbf{-9} \end{array}$