Formulaic Maths Problems

Find $3\begin{pmatrix} -9 \\ 20 \\ 21 \end{pmatrix}-4\begin{pmatrix} -4 \\ -29 \\ 11 \end{pmatrix} + 4\begin{pmatrix} 21 \\ 18 \\ -7 \end{pmatrix} + 4\begin{pmatrix} -17 \\ -8 \\ 16 \end{pmatrix}$.

$\begin{pmatrix} \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar0c0m0}}\hspace{35px}}~} \\ \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar1c0m0}}\hspace{35px}}~} \\ \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar2c0m0}}\hspace{35px}}~} \end{pmatrix} + \begin{pmatrix} \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar0c0m1}}\hspace{35px}}~} \\ \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar1c0m1}}\hspace{35px}}~} \\ \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar2c0m1}}\hspace{35px}}~} \end{pmatrix} + \begin{pmatrix} \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar0c0m2}}\hspace{35px}}~} \\ \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar1c0m2}}\hspace{35px}}~} \\ \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar2c0m2}}\hspace{35px}}~} \end{pmatrix} + \begin{pmatrix} \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar0c0m3}}\hspace{35px}}~} \\ \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar1c0m3}}\hspace{35px}}~} \\ \class{inputBox step1}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Ar2c0m3}}\hspace{35px}}~} \end{pmatrix}$ $\begin{pmatrix} [-27] \\ [60] \\ [63] \end{pmatrix} + \begin{pmatrix} [16] \\ [116] \\ [-44] \end{pmatrix} + \begin{pmatrix} [84] \\ [72] \\ [-28] \end{pmatrix} + \begin{pmatrix} [-68] \\ [-32] \\ [64] \end{pmatrix}$

$= \begin{pmatrix} \class{inputBox step2}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Br0c0}}\hspace{35px}}~} \\ \class{inputBox step2}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Br1c0}}\hspace{35px}}~} \\ \class{inputBox step2}{~\bbox[border:2px solid blue]{\strut\rlap{\class{inputReplace}{Br2c0}}\hspace{35px}}~} \end{pmatrix}$ $= \begin{pmatrix} [5] \\ [216] \\ [55] \end{pmatrix}$