Meu MWE é:
\documentclass{book}
\usepackage{multicol,shortlst}
\raggedright
\setlength{\columnsep}{21pt}%% Space between columns
\setlength{\columnseprule}{2pt}%% Width of rule between columns
\begin{document}
\section{shortlist with 3 enumerate}
\begin{multicols}{2}
\begin{enumerate}
\item The values of should be about $-4$, $-3$. The graph of $y=x$ should approximate a line of gradient~2.
\item The values of should be 0. The graph of $y=x$ is a parabola crossing the $x=-2$ and $x=2$.
\item
\begin{shortenumerate}
\item 3
\item $-7$
\item 5
\item $-3$
\item $\frac{1}{2}$
\item 0
\end{shortenumerate}
\item
\item
\begin{shortenumerate}
$4 +h$, $f'(2) =4$
$2h +3$, $f'(0) =3$
$-6 +h$, $f'(-1) =-6$
\end{shortenumerate}
\item
\begin{shortenumerate}
\item $2x +h -6$, $=2x -6$.
\item It is a concave-up parabola with $x=0$\break and $x=6$.
\item $f'(0) =-6$, $f'(6) =6$.
\item $f'(3) =0$.
\end{shortenumerate}
\item
\begin{shortenumerate}
\item $8 -2x -h$, $=8 -2x$
\item It is a concave-down parabola with $x=0$\linebreak and $x=8$.
\item $f'(0) =8$, $f'(8) =-8$.
\item $f'(4) =0$.
\end{shortenumerate}
\end{enumerate}
\end{multicols}
\end{documento}
\break
e \linebreak
não está funcionando em \item
. Como conseguir isso?