\begin{tikzpicture}[x=.55cm,y=.55cm,font=\footnotesize,>=Latex]
\foreach \shift/\title in {0/{(a) All seven labels},7/{(b) Four surviving labels}}{
 \begin{scope}[xshift=\shift cm]
 \node at (3.2,6.2) {\title};
 \draw[->] (-.4,0)--(7,0) node[right] {\(x\)};
 \draw[->] (0,-.3)--(0,4.85) node[above] {\(x^2\bmod7\)};
 \foreach \x in {0,...,6}{\draw (\x,-.08)--(\x,.08);\node[below] at (\x,-.1) {\x};}
 \foreach \y in {1,...,4}\node[left] at (-.1,\y) {\y};
 \end{scope}
}
\foreach \a/\b/\y in {1/6/1,2/5/4,3/4/2}
 \draw[orange!80!black,dashed,thick] (\a,\y)--(\b,\y);
\foreach \x/\y in {0/0,1/1,2/4,3/2,4/2,5/4,6/1}
 \fill[blue!75!black] (\x,\y) circle(2.5pt);
\begin{scope}[xshift=7cm]
\foreach \x/\y in {0/0,1/1,2/4,3/2}\fill[blue!75!black] (\x,\y) circle(2.5pt);
\foreach \x/\y in {4/2,5/4,6/1}{
 \draw[black!65] (\x-.12,\y-.12)--(\x+.12,\y+.12);
 \draw[black!65] (\x-.12,\y+.12)--(\x+.12,\y-.12);
}
\end{scope}

\end{tikzpicture}