Code:\begin{array}{r@{.}l} 12341 & 43 \\ & 99 \\ 23 & 12 \\ 10 & \\ 938 & 01 \end{array}

Code:\left\{ \begin{array}{r@{+}r@{+}r@{=}l} u & (-v) & w & -1 \\ 3u & & (-9)w & 47 \\ -2u & 5v & 3w & 31 \end{array} \right.

Code:\left\{ \begin{array}{r@{\ +\ }r@{\ +\ }r@{\ =\ }l} u & (-v) & w & -100 \\ 3u & & (-9)w & 47 \\ -2u & 5v & 3w & 31 \end{array} \right.