\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} 24 August 2011
\end{tabular}


\begin{longtable}{p{5cm}p{5cm}p{5cm}}
\vspace{4cm}
\prob  $m+x=b$ for $x$&
\prob  $dy=r$ for $d$&
\prob  $a-b=c$ for $a$\\
\vspace{4cm}
\prob  $mx+b=y$ for $b$&
\prob  $a=c(x-y)$ for $c$&
\prob  $ax+m=c$ for $a$\\
\vspace{4cm}
\prob  $xy-c=d$ for $y$&
\prob  $x(c+\frac{y}{x})=m$ for $y$&
\prob  $y=mx+b$ for $x$\\
\end{longtable}
\prob  The diameter of a circle is twice the radius.  Write a formula for finding the radius $r$ given the diameter $d$ of a circle.
\vspace{4cm}\\
\prob  The circumference of a circle is the diameter times $\pi$.  Write a formula for the circumference $C$ of a circle in terms of the radius $r$.
\vspace{4cm}\\
\prob  Write a formula for the radius $r$ of a circle in terms of the circumference $C$.
\vspace{4cm}
\begin{longtable}{p{5cm}p{5cm}p{5cm}}
\vspace{4cm}
\prob  $a(\frac{x+y}{a})=x$ for $y$&
\prob  $\frac{a}{b}=\frac{c}{b}+1$ for $b$&
\prob  $xy+c=ax+c$ for $x$\\
\vspace{4cm}
\prob  $x=2-x$ for $x$&
\prob  $3y=9$ for $y$&
\prob  $2a-4=8$ for $a$\\
\vspace{4cm}
\prob  $x+y(1+a)=a(y+1)$ for $y$&
\prob  $b+mx=\frac{c}{m}$ for $x$&
\prob  $a+dy=d(a-y)$ for $y$
\end{longtable}
\end{document}