Find the subspace of values that balances the chemical equation in which the antacid calcium hydroxide neutralizes stomach acid (hydrochloric acid) to form calcium chloride and water. $$x_1Ca(OH)_2 + x_2HCl \rightarrow x_3CaCl_2 + x_4H_2O$$
The subspace = span{A} where

${\rm A} =$

$\left.\vphantom{\begin{array}{c}\!\strut\\\!\strut\\\!\strut\\\!\strut\\\!\strut\\\end{array}}\right[$ $\left.\vphantom{\begin{array}{c}\!\strut\\\!\strut\\\!\strut\\\!\strut\\\!\strut\\\end{array}}\right]$

.