% http://tex.stackexchange.com/q/338165
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{leading,microtype}
\usepackage[french]{babel}

\usepackage{tasks}
\usepackage{xsim}
\usepackage{tcolorbox}
\tcbuselibrary{breakable, skins}
\settasks{ label = \arabic*. }

\DeclareExerciseEnvironmentTemplate{boxed}{%
  \tcolorbox[
    enhanced ,
    attach boxed title to top center = {yshift=-7.5pt} ,
    colback = white , colbacktitle = white ,
    coltitle = black , colframe = black ,
    boxed title style = { colframe = white } ,
    fonttitle=\bfseries,
    sharp corners=all,
    breakable,
    title=
      \XSIMmixedcase{\GetExerciseName}%
      \IfInsideSolutionF{%
        ~\GetExerciseProperty{counter}%
        \IfExercisePropertySetT{subtitle}{: \GetExerciseProperty{subtitle}}%
      }%
  ]
}{\endtcolorbox}

\xsimsetup{
  exercise/template = boxed ,
  solution/template = boxed ,
  solution/print =  true
}

\leading{15pt}

\newcommand*\complement{\overline}
\newcommand*\union{\cup}
\newcommand*\intersection{\cap}
\newcommand*\set[1]{\{#1\}}

\begin{document}

\begin{exercise}[subtitle=Set Calculus]
  Soient $E=\set{1,2,3,4,5,6,7}$ et $A$, $B$, $C$ et $D$ quatre parties de E
  d\'efinies par $A=\set{1,2,3,4}$, $B=\set{4,5,6,7}$, $C=\set{1,3,5,7}$ et
  $D=\set{2,3,4,5,6}$.
  \begin{tasks}(2)
    \task Calculer $\complement{A}$.
    \task Calculer $(A\union B) \intersection (C\union D)$.
    \task Calculer $(A\intersection B) \union (C\intersection D)$.
    \task Calculer $\complement{(\complement{A}\union B)} \union
      \complement{(C\intersection D)}$.
  \end{tasks}
\end{exercise}
\begin{solution}
  \begin{tasks}(2)
    \task $\set{5,6,7}$
    \task $E$
    \task $\set{3,4,5}$
    \task $\set{1,2,3,4,6,7}$
  \end{tasks}
\end{solution}

\end{document}