\documentclass[a4paper]{article}
%\usepackage{mathptmx}
% from kantlipsum
\newcommand\txt{Let us suppose that the noumena have nothing to do
with necessity, since knowledge of the Categories is a posteriori.}
\newcommand\mth{$x^{(n)}_j$, $B^{(n)}_j$, $B^{U(n)}_j$}
\newcommand\mths{$x^{\smash{(}n\smash{)}}_j$,
$B^{\smash{(}n\smash{)}}_j$, $B^{U\smash{(n)}}_j$}
\begin{document}
\txt{} \mth{} \txt{}
\txt{} \mth{} \txt{}
\txt{} \mths{} \txt{}
\end{document}