\documentclass[10pt]{amsart}
\usepackage[margin=1in]{geometry} 
\usepackage[parfill]{parskip}% Begin paragraphs with an empty line rather than an indent
\usepackage{graphicx}
\usepackage{amssymb}% do not use with mtpro2 except lite version
%SetFonts
% libertine+newtxmath
\usepackage[ttscaled=.9375]{libertine}
\usepackage[T1]{fontenc}
\usepackage{textcomp}
%\usepackage[varqu,varl]{zi4}% inconsolata
%\usepackage{amsmath,amsthm}
\usepackage[libertine,bigdelims]{newtxmath}
\useosf
\usepackage[supstfm=libertinesups,%
  supscaled=1.2,%
  raised=-.13em]{superiors}
%SetFonts
\title{Brief Article}
\author{Michael Sharpe}
\date{\today}  % Activate to display a given date or no date

\begin{document}
\maketitle
{\tt test of monospaced typewriter}\\
%\setbox0\hbox{{\usefont{T1}{pcr}{m}{n}x}}\showthe\wd0
\setbox0\hbox{\tt x}\showthe\wd0
\end{document}  