\begin{columns}
\column{.5\textwidth}
\begin{block}{Answered Questions}
How many primes are there?
\end{block}
\column{.5\textwidth}
\begin{block}{Open Questions}
Is every even number the sum of two primes?
\end{block}
\end{columns}

\begin{figure}
\centering
\mbox{\subfigure{\includegraphics[width=3in]{fig1.pdf}}\quad
\subfigure{\includegraphics[width=3in]{fig2.pdf} }}
\caption{Text pertaining to both graphs ...} \label{fig12}
\end{figure}

\begin{figure}[ht]
\begin{minipage}[b]{0.5\linewidth}
\centering
\includegraphics[scale=0.15]{1.png}
\end{minipage}
\hspace{0.5cm}
\begin{minipage}[b]{0.5\linewidth}
\centering
\includegraphics[scale=0.15]{2.png}
\end{minipage}
\hspace{0.5cm}
\begin{minipage}[b]{0.5\linewidth}
\centering
\includegraphics[scale=0.15]{3.png}
\end{minipage}
\end{figure}