documentclass{article}
usepackage{systeme}
begin{document}
[
systeme{3+2t+s=x,s+2=y,1+t+2s=z}
]
end{document}

documentclass{article}
usepackage{amsmath}
usepackage{systeme}

begin{document}
[
systeme[xyzts]{3+2t+s=x,s+2=y,1+t+2s=z}
]
end{document}