\documentclass[12pt,reqno]{amsart} 

\usepackage{amsmath,amssymb,amsfonts,amsthm,mathrsfs}
\usepackage{graphicx}
\usepackage{enumerate}
\usepackage[top=1in,bottom=1in,left=1in,right=1in]{geometry}
\usepackage{circuitikz}

\renewcommand{\baselinestretch}{1.25}

\newtheorem{thm}{Theorem}
\newtheorem{ex}{Exercise}
\newtheorem*{defn}{Definition}

\newcommand{\PS}{\mathscr{P}}

\begin{document}

\begin{flushright}
Your Name Here\\
Math 220\\
HW \# 10\\
\today
\end{flushright}

%Please write your solutions in the designated solution area!

\begin{ex}
Let $A=\{2,3,4\}$ and $B=\{6,8,10\}$ and define a binary relation $R$ from $A$ to $B$ by $xRy$ if and only if $x|y$.
\begin{enumerate}[$(a)$]
\item Is $4R6$? Is $4R8$? Is $(3,8)\in R$? Is $(2,10)\in R$?
\item Write $R$ as a set of ordered pairs.
\end{enumerate}
\end{ex}

\begin{proof}

\end{proof}

\begin{ex}
Let $n\in\mathbb{N}$. Define a relation $\sim$ on $\mathbb{Z}$ by $a\sim b$ if and only if $a\equiv b\mod n$. Show that $\sim$ is reflexive, symmetric, and transitive.
\end{ex}

\begin{proof}

\end{proof}

\end{document}