fbox typing in Latex

Question

Whats the Latex code for inserting a small boxes at the end of a remark sentence like the ones in the image above?

Answer 1

The remarks of the image are proof environments of amsthm. No need to type directly the \qedsymbol:

\documentclass{article}
\usepackage{lipsum,parskip}
\usepackage{amsthm,amssymb}
\begin{document}
\begin{proof}
This is classwork, straight from the lectures notes.
\end{proof}
\renewcommand\proofname{Remark}
\begin{proof}
This is classwork, straight from the lectures notes.
\end{proof}
\begin{proof}
\lipsum[1][1-5]
\end{proof}
With \qedsymbol\ changed to \renewcommand\qedsymbol{$\boxtimes$}\qedsymbol:
\begin{proof}[Whatever]
\lipsum[2][1-3]
\end{proof}
\end{document}