Q: How to align enumerate and add answer to exercises? I want to alight enumerate my Exercises. My old way is
\begin{ex}
Find the volume of the following pyramids $ABCD$

\begin{enumerate}[\quad 1)]
\item $A(1; 2; 3)$, \quad $B(2; 1; -2)$, \quad $C(-1; -4; 3)$, \quad $D(2; 1; -5)$;

\hfill Answer. 4.
\item $A(1;-2;-4)$, \quad $B(-2;-1;0)$, \quad $C(3; 4;-2)$, \quad $D(5; 5; -5)$;

\hfill Answer. 5.
\item $A(3; 2; 1)$, \quad $B(2; 4; 6)$, \quad $C(1; 5; 3)$, \quad $D(5; 4; 3)$.

\hfill Answer. 6.
\end{enumerate}
\end{ex}


Now I want to align coordinates of the vertices A, B, C, D. I tried
\begin{ex}
 Find the volume of the following pyramids

\setcounter{eqn}{0}
\begin{alignat*}{6}
\num&& A(1; 2; 3), \qquad& B(2; 1; -2),\qquad& C(-1; -4; 3),\qquad& D(2; 1; -5); \\
\num&& A(-3; -2; -1), \qquad&  B(2; 4; 6),\qquad& C(1; 5; 3), \qquad& D(5; 4; 3).
\end{alignat*}
\end{ex}


How can I align to all vertices A, B, C, D to the left (none right with A and C like the second picture) and how can I add answer to every item like my old way?
My full code
\documentclass{article}
\usepackage{amsmath}
\newcounter{eqn}
\usepackage{enumerate}
\renewcommand*{\theeqn}{\arabic{eqn})}
\newcommand{\num}{\refstepcounter{eqn}\text{\theeqn}\quad}
\usepackage{amsthm}
\theoremstyle{definition} 
\newtheorem{ex}{Exercise}
\begin{document}
\begin{ex}
Find the volume of the following pyramids $ABCD$
\begin{enumerate}[\quad 1)]
\item $A(1; 2; 3)$, \quad $B(2; 1; -2)$, \quad $C(-1; -4; 3)$, \quad $D(2; 1; -5)$;

\hfill Answer. 4.
\item $A(1;-2;-4)$, \quad $B(-2;-1;0)$, \quad $C(3; 4;-2)$, \quad $D(5; 5; -5)$;

\hfill Answer. 5.
\item $A(3; 2; 1)$, \quad $B(2; 4; 6)$, \quad $C(1; 5; 3)$, \quad $D(5; 4; 3)$.

\hfill Answer. 6.

\end{enumerate}
\end{ex}

\begin{ex}
Find the volume of the following pyramids
\setcounter{eqn}{0}
\begin{alignat*}{6}
  \num&& A(1; 2; 3), \qquad& B(2; 1; -2),\qquad& C(-1; -4; 3),\qquad& D(2; 1; -5); \\
\num&& A(-3; -2; -1), \qquad&  B(2; 4; 6),\qquad& C(1; 5; 3), \qquad& D(5; 4; 3).
\end{alignat*}
\end{ex}
\end{document}


A: Is it like this?
\documentclass{article}
\usepackage{amsmath}
\newcounter{eqn}
\usepackage{enumerate}
\renewcommand*{\theeqn}{\arabic{eqn})}
\newcommand{\num}{\refstepcounter{eqn}\text{\theeqn}\quad}
\usepackage{amsthm}
\theoremstyle{definition}
\newtheorem{ex}{Exercise}

\newcommand*{\mybox}[1]{%
    \makebox[1in][l]{$#1$}
    }
\begin{document}
\begin{ex}
Find the volume of the following pyramids $ABCD$
\begin{enumerate}[\quad 1)]
\item \mybox{A(1; 2; 3),} \mybox{B(2; 1; -2),} \mybox{C(-1; -4; 3),} \mybox{D(2; 1; -5);}

\hfill Answer. 4.
\item \mybox{A(1;-2;-4),} \mybox{B(-2;-1;0),} \mybox{C(3; 4;-2),} \mybox{D(5; 5; -5);}

\hfill Answer. 5.
\item \mybox{A(3; 2; 1),} \mybox{B(2; 4; 6),} \mybox{C(1; 5; 3),} \mybox{D(5; 4; 3).}

\hfill Answer. 6.

\end{enumerate}
\end{ex}

\begin{ex}
Find the volume of the following pyramids
\setcounter{eqn}{0}
\begin{alignat*}{6}
  \num& A(1; 2; 3), && \quad B(2; 1; -2),&&\quad C(-1; -4; 3),&&\quad D(2; 1; -5); \\
\num& A(-3; -2; -1), &&\quad  B(2; 4; 6),&&\quad C(1; 5; 3), &&\quad D(5; 4; 3).
\end{alignat*}
\end{ex}
\end{document}


