TeX source:
\begin{align}4x+3y & = 2400 & \qquad 2x+y & = 1000 \\[1em] x \quad & | \quad y & \qquad x \quad & | \quad y \\ \hline 0 \quad & | \quad 800 & \qquad 0 \quad & | \quad 1000 \\ 600 \quad & | \quad 0 & \qquad 500 \quad & | \quad 0 \\ \end{align}