A table spread past the edges of the page

Question

Why is the following table wider than the page?!

After comments from two members from this site, I included more code from the original file. It seems that the tabular environment in the first problem is prompting TeX to artificially stretch the table in the last problem.

\documentclass{amsart}


\usepackage{tikz}
\usetikzlibrary{calc,intersections}


\usepackage{makecell}


\begin{document}


\noindent \textbf{1.) }Compute the following differences. Express each difference as a fraction for which the only common divisor of the numerator and denominator is 1. \\ \\
\noindent \hspace*{2em}
\setlength{\tabcolsep}{0.75in}
\setlength{\extrarowheight}{3ex}
\begin{tabular}{@{}r@{}lr@{}lr@{}l}
\textbf{i.) }   &   $\displaystyle{\frac{1}{2} - \frac{1}{3}}$
&
\textbf{ii.) }  &   $\displaystyle{1 - \frac{1}{3}}$
&
\textbf{iii.) } &   $\displaystyle{\frac{11}{18} - \frac{22}{45}}$ \\[1.2\normalbaselineskip]
\textbf{iv.) }  &   $\displaystyle{\frac{27}{14} - \frac{12}{35}}$
&
\textbf{v.) }   &   $\displaystyle{\frac{16}{27} - \frac{32}{81}}$
&
\textbf{vi.) }  &   $\displaystyle{\frac{21}{10} - \frac{21}{100}}$
\end{tabular}
\vskip0.25in

\vfill
\pagebreak


\noindent \textbf{14.) }What is the perimeter of the following triangle?
\vskip0.2in

\noindent \hspace*{\fill}
\begin{tikzpicture}


%Triangle ABC is drawn. The lengths of AB, AC, and BC are to be 8, 10, and 12, respectively.
%(The measure of the angle between AB and AC is arc cos(1/8).)
\coordinate (A) at (0,0);
\coordinate (B) at (5,0);
\coordinate (C) at ({acos(1/8)}:4);
\draw (A) -- (B) -- (C) -- cycle;



%The lengths of the sides of the triangle are typeset.
\node[anchor=north, inner sep=0, font=\footnotesize] at ($($(A)!0.5!(B)$) +(0,-0.15)$){$10$};
\node[anchor={acos(1/8)-90}, inner sep=0, font=\footnotesize] at ($($(A)!0.5!(C)$) +({acos(1/8)+90}:0.15)$){$8$};
\draw let \p1=($(B)-(C)$), \n1={atan(\y1/\x1)} in node[anchor={\n1-90}, inner sep=0, font=\footnotesize] at ($($(B)!0.5!(C)$) +({\n1+90}:0.15)$){$12$};


\end{tikzpicture}
\hspace{\fill}
\vskip0.25in

\noindent The following table, describing the Preston City workforce, is missing some data entries. Based on the information in the table, how many women in the Preston City workforce are unemployed?
\begin{tabbing}
\hspace*{3em} \= \hspace{2.5in} \= \kill
\> \textbf{a.) }500     \> \textbf{b.) }1000 \\
\> \textbf{c.) }1500    \> \textbf{d.) }2000 \\
\> \textbf{e.) }2500
\end{tabbing}
\vskip0.2in

\noindent \hspace*{\fill}
\setlength\extrarowheight{2pt}
\begin{tabular}{|| c | c | c !{\vrule width0.8pt}c ||} \hline
\multicolumn{4}{|| c ||}{{\bf Residents of Preston City}} \\ \Xhline{0.8pt}
            &   Employed    &   Unemployed  &   Total \\ \hline
    Men     &   27,000      &               &   \\ \hline
    Women   &               &               &   21,500 \\ \Xhline{0.8pt}
    Total   &   48,000      &               &   50,500 \\ \hline
\end{tabular}
\hspace{\fill}

\end{document}