Write out the matrix equation for this given system of equations
$\displaystyle {\left\lbrace\begin{array}{ccccccc} {6}{r}&+&{2}{a}&+&{3}{m}&=&{200}\\{4}{r}&+&{a}&+&{2}{m}&=&{300}\\{3}{r}&+&{a}&+&{m}&=&{400}\end{array}\right.}$

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