Fix variable name [closes #59]

chapter06.tex

@@ -34,7 +34,7 @@ What is the minimum number of coins needed?
 
 For example, if the coins are the euro coins (in cents)
 \[\{1,2,5,10,20,50,100,200\}\]
-and $x=520$,
+and $n=520$,
 we need at least four coins.
 The optimal solution is to select coins
 $200+200+100+20$ whose sum is 520.
@@ -677,4 +677,4 @@ character & codeword \\
 \texttt{C} & 10 \\
 \texttt{D} & 111 \\
 \end{tabular}
-\end{center}
+\end{center}