Solution
= Solution
For $k=1$, the required right-hand matrix has twice the first row of $A$, the same second row, and twice the third row. Left multiplication scales rows, so
$$
\boxed{B=\operatorname{diag}(2,1,2).}
$$
Equivalently, right multiply the given equation $BA=C$ by $A^{-1}$ to obtain the same answer.