\documentclass[compose,siunitx]{exam-n}
\begin{document}
\begin{question}{20} \author{Frieda Bloggs}
\shout{Dummy question}
\part Show that, under the action of gravity alone, the scale size
of the Universe varies according to
\[
\ddot{R}=-\frac{4\pi G \rho_0}{3R^2}.
\]
Is $\ddot{R}=\Diffl*[2]{R}{t} > \SI{10}{\astronomicalunit. s^{-2}}$?
\partmarks*{4}
\begin{solution}
This can be solved by remembering the answer.
\end{solution}

\part Explain the nature of being.
\partmarks{16}
\begin{solution}
Om.
\end{solution}
\end{question}
\end{document}
