\documentclass[11pt]{article}
\usepackage{amsmath, amsthm, amssymb, amsthm, units, full page}
\usepackage{longtable}

\newcounter{prob_num}
\setcounter{prob_num}{1}
\newcommand{\prob}{\arabic{prob_num})  \stepcounter{prob_num}}

\begin{document}


\begin{tabular}{lr}
	Name:\underline{\hspace{8cm}}  & Math 095 Skill-Builder 1 \\
	& \hspace{3cm} 31 January 2012
\end{tabular}

\textbf{Section I.} Use one inversion.\\
\vspace{0.5cm}
\begin{longtable}{p{5cm}p{5cm}p{5cm}}
\vspace{5cm}
\prob  $m+x=b$ for $x$&
\prob  $dy=r$ for $d$&
\prob  $a-b=c$ for $a$\\
\vspace{5cm}
\prob  $mx+b=y$ for $b$&
\prob  $a=c(x-y)$ for $c$&
\prob  $\frac{ax}{m}=c$ for $a$\\
\vspace{5cm}
\prob  $a=c\frac{1}{(x-y)}$ for $c$&
\prob  $\frac{m}{x}=\frac{a}{x+y}$ for $a$
\end{longtable}
\pagebreak
\textbf{Section II.} Use two inversions.\\
\vspace{0.5cm}
\begin{longtable}{p{5cm}p{5cm}p{5cm}}
\vspace{5cm}
\prob  $y=mx+b$ for $x$&
\prob  $xy-c=d$ for $y$&
\prob  $y+\frac{c}{m}=x$ for $c$\\
\vspace{5cm}
\prob  $\frac{a}{b}(m+x)=a$ for $m$&
\prob  $x(y+\frac{c}{x})=m$ for $y$&
\prob  $\frac{b+c}{x-y}=mx$ for $b$\\
\vspace{5cm}
\prob  $\frac{b(a-x)}{c}=x$ for $a$&
\prob  $\frac{c(b+x)}{d}=a-y$ for $x$
\end{longtable}
\vspace{5cm}
\textbf{Section III.} Use distribution and inversion.\\
\vspace{0.5cm}
\begin{longtable}{p{5cm}p{5cm}p{5cm}}
\vspace{5cm}
\prob  $ay+by=x$ for $y$&
\prob  $dy+c=ad+c$ for $d$&
\prob  $x+cy=a(c+m)$ for $c$\\
\vspace{5cm}
\prob $y(1+a)=a(1+y)$ for $y$
\end{longtable}
\end{document}