begin{center}

begin{minipage}{.4textwidth}
includegraphics[scale=.5]{StaircaseWalk1x1.png}
captionof{figure}{1x1 Grid}
end{minipage}
hspace{1.2cm}
begin{minipage}{.4textwidth}
includegraphics[scale=.5]{StaircaseWalk2x2.png}
captionof{figure}{2x2 Grid}
end{minipage}

vspace{1.2cm}

begin{minipage}{.4textwidth}
includegraphics[scale=.65]{StaircaseWalk3x3.png}
captionof{figure}{3x3 Grid}
end{minipage}

end{center}