Answer
$$B=\left[\begin{array}{r}{1}&{0} \\ {1}&{0} \end{array}\right], \quad C=\left[\begin{array}{r}{0}&{0} \\ {3}&{0} \end{array}\right] $$
Work Step by Step
Let $$B=\left[\begin{array}{r}{1}&{0} \\ {1}&{0} \end{array}\right], \quad C=\left[\begin{array}{r}{0}&{0} \\ {3}&{0} \end{array}\right] $$
we get that
$$AB=\left[\begin{array}{r}{2}&{1} \\ {6}&{3} \end{array}\right]\left[\begin{array}{r}{1}&{0} \\ {1}&{0} \end{array}\right]=\left[\begin{array}{r}{3}&{0} \\ {9}&{0} \end{array}\right]$$
and
$$AC=\left[\begin{array}{r}{2}&{1} \\ {6}&{3} \end{array}\right]\left[\begin{array}{r}{0}&{0} \\ {3}&{0} \end{array}\right]=\left[\begin{array}{r}{3}&{0} \\ {9}&{0} \end{array}\right].$$
