Thank you for your answer. This is what I did:
\documentclass[12p]{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{graphicx}
\begin{document}
\begin{tabular}{ l c r }
$2x+3=7$ & $5x-2=3$ & $2x+7=11$\\
$6x+1=9$ & $6x+1=9$ & $-4x-5=14$ \\
$2x+3=7$ & $5x-2=3$ & $2x+7=11$ \\
\end{tabular}
\end {document}
And it produced This.
Now, How would I do to number them automatically with a bold font?
Also, how would I do to increase horizontal spaces?