\documentclass[12pt,letterpaper, onecolumn]{exam}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[lmargin=71pt, tmargin=1.2in]{geometry} %For centering solution box
\lhead{Leaft Header\\}
\rhead{Right Header\\}
% \chead{\hline} % Un-comment to draw line below header
\thispagestyle{empty} %For removing header/footer from page 1
\begin{document}
\begingroup
\centering
\LARGE Subject\\
\LARGE Assignment Number\\[0.5em]
\large \today\\[0.5em]
\large Author\par
\large Roll Number\par
\large Class/Batch/Section\par
\endgroup
\rule{\textwidth}{0.4pt}
\pointsdroppedatright %Self-explanatory
\printanswers
\renewcommand{\solutiontitle}{\noindent\textbf{Ans:}\enspace} %Replace "Ans:" with starting keyword in solution box
\begin{questions}
\question[1 Mark] Q1?\droppoints
\begin{solution}
A1.
\end{solution}
\question[2 Marks] Q2?
\begin{parts}
\part Part. a
\part Hint: These can be nested further\droppoints
\end{parts}
\begin{solution}
A2.
\begin{parts}
\part Ans. for (a)
\part Solution for (b)
\end{parts}
\end{solution}
\pagebreak %Not necessary
\question[Type anything here] Q3?\droppoints
\begin{solution}
A3.
\end{solution}
\end{questions}
\end{document}
